In Sarga 18 of the Kishkindha Kanda of the Valmiki Ramayana, Rama explains to a dying Vali as to why He attacked him behind his back. Rama categorically explains all the questions put by Vali in the last chapter from the viewpoint of scriptures (Manusmriti) that lays down the principles of Sanatana Dharma. Vali finally concludes that there is someone superior to him and thus seeks refuge in Rama.
No. It is impossible. The Manusmṛiti mentions the fall of Kṣatriya groups that we know happens long after Treta Yuga. That, the Parāśara (possibly Pārāsara) Smṛiti saying it is for Satya Yuga and it mentioning the Sarasvati river as a landmark means it has to be talking about a future Satya Yuga. It makes no sense to apply to Rama Rajya.
शनकैस्तु क्रियालोपादिमाः क्षत्रियजातयः । वृषलत्वं गता लोके ब्राह्मणादर्शनेन च ॥ ४३ ॥
śanakaistu kriyālopādimāḥ kṣatriyajātayaḥ | vṛṣalatvaṃ gatā loke brāhmaṇādarśanena ca || 43 ||
But by the omission of the sacred rites, and also by their neglect of Brāhmaṇas, the following Kṣatriya castes have gradually sunk to the position of the low-born.—(43)
पौण्ड्रकाश्चौड्रद्रविडाः काम्बोजा यवनाः शकाः । पारदापह्लवाश्चीनाः किराता दरदाः खशाः ॥ ४४ ॥
pauṇḍrakāścauḍradraviḍāḥ kāmbojā yavanāḥ śakāḥ | pāradāpahlavāścīnāḥ kirātā daradāḥ khaśāḥ || 44 ||
The Puṇḍrakas, the Coḍas, the Draviḍas, the Kāmbojas, the Yavanas, the Śākas, the Pāradas, the Pahlavas, the Cīnas, the Kirātas, the Daradas and the Khaśas.—(44)
P.S. This timing is a good reason not to trust the Agni Purana's quoting of the laws of Manu from Pushkara. As the first Manu writing it means it would be highly unlikely he actually got emancipation as the common translation suggests as he would still be alive near the present.
Short answer to your question is yes and there are more proves than just what you mentioned some references being direct and others indirect. Long answer with references waits ahead.
I) DASRATH RAJYA:
To know Ramrajya one must first know what was Dasrath Rajya as well and as the article progresses they shall understand why I have included Dasrath Rajya in this. The Valmiki Ramayan Bal Khand Sarga 6 describes the kingdom of Raja Dasrath stating that in his kingdom as a kingdom ruled as per the Dharma Shastras, it is stated the kingdom was full of scholars learned in the various scriptures, all the citizen law abiding and honest, crime rate was absolutely zero and there were no atheists and lustful people in the country. Special emphasis must be given on slok 5 of this sarga which states that "Raja Dasrath while dwelling in the city of Ayodhya protected the world, like Manu, the foremost protector of mankind" which is a clear reference to the fact that Manusmriti was the law book used in time of Raja Dasrath otherwise the comparison would not have been made, a fact which is proven in the The Valmiki Ramayan states in Bala Khand Sarga 70 sloka 16 that Ikshvaku was the founder of this ancient dynasty in which Shri Ram was born while it is stated in sloka 21 of this same Sarga that Vaivastava Manu was the father of Ikshvaku. It is later stated in the Valmiki Ramayana Ayodhya Khand Sarga 2 sloka 6 that King Dasrath who was father of Shri Ram ruled the kingdom as per the laws ordained by his forefathers which is a clear reference to the fact that the laws of Manu were used in his rule and the comparison stated earlier was made on this exact basis.
II) RAMRAJYA SWAROOP:
The Valmiki Ramayan describes Ramrajya in the Uttar Khand Sarga 99 sloka 11-14 as being full of prosperity where all creatures stayed in harmony, no one died before time, everyone was in perfect condition, there were no natural calamities and seasons came and went away on time without causing hardships or disasters.
The Ananda Ramayan states in Sara Khand Sarga 12 slok 117 that states Shri Ram throughout his life enacted Dharma and its doctrines and spread rules of the Vedas and describes Ramrajya in Yatra Khand Sarga 3 sloka 15-17 stating that in Ramrajya there was no obstruction in ruling the kingdom, everyone was happy and prosperous, there were no calamities and food was produced in abundance, crime rate was absolutely zero. Ramrajya has been described in its full glory in the Rajya Khand Sarga 15 however stating the exact statements here shall be too long for this Sarga has a total of 86 slokas hence only the important points not available in the other mentioned references shall be provided; this Sarga apart from attributing the same qualities to Ramrajya as stated in the other references already given mentions in slok 2-3 that the kingdom had an extremely strong army, in slok 16 that no person in the kingdom consumed any intoxicants, in slok 21-22 that the various forts and the capital was well protected with strategic defenses, in slok 33 that Shri Ram had an excellent spy network or in simple terms the best intelligence department, in slok 55 that there was no polygamy in his kingdom. In the Rajya Khand Sarga 18 slok 54 Shri Ram himself ordains that authority of Bramhans in matters of decision of dharma must be protected and ensured by all kings. There is yet another reference vital for this article in the Manohar Khand Sarga 4 slok 273 which declears Manu to be the authority on Dharma and hence in term directly bears witness to the fact that the Manusmriti was used in Ramrajya as is evident by viewing this verse in light of the other mentioned references which all unanimously states that in Ramrajya Dharma was strictly followed.
The Adbhut Ramayan describes Ramrajya in Adhay 27 sloka 8-9 stating that Shri Ram after coming back to Ayodhya after war against Ravan cleansed the earth of Adharmis and conducted many yajnas. This states though slightly indirectly that Dharma was strictly followed in Ramrajya.
The Adhyatma Ramayan describes Ramrajya in Chapter 4 verse 21-22 stating that in Ramrajya everyone was well nourished, happy and rich, the trees and fields produced food in abundance, everyone followed Dharma and the husbands and wives were strictly dedicated to each other with zero signs of adultery.
The Ramcharitmanas describes Ramrajya in Uttar Khand verses 20-23 stating that in Ramrajya there was no fear and disease of any kind, everyone followed their duties as per the scriptures and obtained happiness, there were no untimely deaths and natural disasters, husbands and wives were faithful to each other and there were absolutely no crime in the kingdom.
To put it all in short Ramrajya was the perfect period of governance where food was in abundance, everyone was prosperous, Dharma and scriptures was follow strictly, crime rate and adultery were non existent, there were no atheists and Manusmriti was the book of law used in this ideal kingdom.
III) THE COMMON LINK:
Why it was stated in the point II that to know Ramrajya first Dasrath Rajya must be known shall be visible in this point. As stated earlier in point II, Raja Dasrath followed and used Manusmriti to govern his kingdom. What must be known now is that as per the Valmiki Ramayana Ayodhya Khand Sarga 2 sloka 46 Shri Ram governed various matters using the same laws as that of his ancestors hence as Dasrath which in turn only solidifies the fact proved in the earlier point that Shri Ram used the Manusmriti to rule his kingdom. One must also be made aware of the fact that Swyambhu Manu who was the first of the 14 Manus was the composer of the Manusmriti and this Manusmriti was followed by the other Manus as per the Manusmriti Chapter 1 verse 63 which in turn when combined with point II shows again that what we call as Manusmriti which was written by Swyambhu Manu is the only Manusmriti and debunks reformist claims of some other documents being used.
It must also be noted that in the Manusmriti Chapter 7 which deals with conduct to be observed by kings states in verse 3 that when lawlessness and chaos was prevalent and all creatures were in terrible fear, Ishvar created king and monarchy to put an end to their misery and bring back order by establishing a peaceful and balanced society, stating in verses 14-15 that Ishvar created the institution of punishment to ensure an ideal condition prevails through its application which will prevent chaos and further stating in verse 31 that those who follow their duties as per command of the scriptures must not be punished, which in turn states than an ideal monarchy is governed as per scriptures and is crime free which in turn is the exact same description we find of the Ramrajya. The Manusmriti describes atheists as those who abuse and are against the Vedas in Chapter 2 verse 11 and states in Chapter 4 verse 61 that countries which has atheists and Dharma is not observed as per scriptures must be avoided which in turn naturally implies that the kingdom free from atheists and governed as per scriptures is stated to be ideal in view of Manu Maharaj. Yet another common link is the Valmiki Ramayan Ayodhya Khand Sarga 100 where Shri Ram while advising Bharat on how to govern kingdom gives advise strictly based on the Manusmriti, a fact than can be observed clearly by making a comparative study of the mentioned reference and the Manusmriti. Bramhans being authority in Dharma stated in the Ananda Ramayan Rajya Khand Sarga 18 slok 54 is also confirmed by the Manusmriti Chapter 1 verse 98. There are many more such comparative references that can be provided apart from direct evidence to prove that Manusmriti indeed was used as the Dharma Shastra in Ramrajya and for all who actually want Ramrajya, Manusmriti holds a very close position.
JAI VEERBHADRA JAI SHANKARACHARYA
Credits of the writing and compilation belongs to: Jalandhar.
Yes only not current Manusmriti. Otherwise Lord would have killed or at least punished Shabri (low caste) for performing Tapasya. Instead he preferred her over other saints.
Current Manusmriti refers to Manu in third person and has caste laws which would have debarred not just Shabri, but also Ved Vyas, Jabala, Vishwamitra and many more than 100 people whose life we know details about from getting initiation!!
The decision is that—‘one born to an Ārya from a Non-Ārya woman may be an Ārya in quality; but one born to a Non-ārya even from an Ārya woman is always Non-Ārya’ (10.67)
The settled law is that both these are unfit for the sacraments (10.68)
So we would not have the 4 Vedas nor Upanishads nor Puranas nor Itihas if these laws were followed. We also know that Manu had progeny that repeatedly and freely changed their caste. So Lord Ram was quoting from the original smriti.
If he was quoting from current one, then he followed hierarchy of scriptures where Vedas, Puranas, Rahasyas, Itihasas etc. are more authoritative so he discarded contradicting verses.
It is also common knowledge that Manu had children, grandchildren etc. who repeatedly changed Varnas very freely. So again, it's totally impossible this was completely followed in Ram Rajya