Do scriptures change over time? Or they're static but different for each Yuga? Can customs of one Yuga be ridiculed by people in earlier or next Yuga?

Question

It is well known that laws & customs change over time, according to people, society and events.

Some people claim that religious scriptures also change over time.

But the wise say that religious scriptures do not change, but they already take into account all possible changes (combinations of people/society/events for all yugas) and codify those laws at the beginning.

For e.g. If a law states:

1. [2015] Stop on Red light.

Then in 2016, it gets amended to:

2. [2016] Stop on Red light, except if you hear ambulance, in which case, give way.

Then in 2017, it gets amended further to:

3. [2017] Stop on Red light, except if you hear ambulance, in which case, give way, but only if ambulance driver is within 20 ft of you.

In above case we can say 'The law changes over time'.

But if a law says:

1. Stop on Red light, except if you hear ambulance, in which case, give way, but only if ambulance driver is within 20 ft of you, and if he honks twice to indicate you to move, (and other possible combinations)

In above case we can say 'The law does not change over time. It accounts for all possible changes ahead of time'.

Do scriptures fall under first or second category ?
If second, is there a different Smriti to be followed in each Yuga ?
If different, is there a hierarchy or gradation of rules, going from strict to relaxed from Krita to Kali ?
If gradation, is it because the scriptures/rishis are 'outdated', or because the society/people become 'degraded' ?
If latter, then is it acceptable for someone to follow rules of a previous Yuga ? For e.g. Crossing seas is banned in Kali but not in previous Yugas. Same with Niyoga.
If above unacceptable, is it acceptable to ridicule others for following customs of their current relaxed/degraded Yuga instead of a strict/exalted previous Yuga's rules ?
If above unacceptable, is the opposite OK - is it acceptable to ridicule others for following customs of a strict/exalted previous Yuga instead of their current relaxed/degraded Yuga's rules ?

e.g. people of Treta Yuga might ridicule those of Krita Yuga for always being engaged in Dhyana. While those in Krita Yuga might ridicule future inhabitants of Treta Yuga for always being engaged in Yagna.
Similarly, people of Kali Yuga might ridicule those of Dwapara Yuga for engaging in child marriage, being faithful/virgin, following varna separation etc. While those in Dwapara Yuga might ridicule future inhabitants of Kali Yuga for late marriages, multiple-sexual partners, varna-sankara (caste-mixing) etc.

When "social reformers" bring changes to constitutional laws (inherently according to scripturally mandated amendments for each Yuga), should they do so by deriding old scriptures, or by deriding new people?

e.g. When Sati/Child-marriage was banned long back, or when Adultery/Homosexuality was legalized recently, should it be done by stating :
'Old Scriptures are regressive/patriarchal/evil' ?
or by stating :
'New People are degraded/weak/animalistic' ?

Answer 1

Parashara Smriti answers these questions. Quoting verses from the first Chapter of the text:

17. " All laws arose in the Krita age ; all have vanished in the Kali age. Expound a part of the rules of conduct fit for the four castes, such as are common (to all)

18. " In each Kalpa (the deities) Brahma and "Vishnu and Shiva, and the expounders of the Veda, the Smrithis invariably perish, and are born again.

All the Laws pertaining to Dharma arose in the Krita Yuga, so they are fixed. They don't change with time because they were already created at the beginning.

But for different Yugas these Laws are slightly different.

21. " The author of the Veda there is none ; (he) the fourfaced (God), at each succeeding revolution of a Kalpa, recalls to mind the Veda ; and so does Manu remember the law (at each succeeding revolution of a Kalpa).

22. " In conformity to the character of the age, the rules of law (suitable) for men differ from age to age. The rules for the Krita differ from the Treta rules ; the Dvapara laws are not identical with the Kali rules.

If second, is there a different Smriti to be followed in each Yuga ?

Yes as per the following verse:

24. " For the Krita are suited the laws of Manu ; for the Treta, those by Gautama (are) prescribed ; for the Dvapara those by Shank and Likhita ; for the Kali, those by Parasara are prescribed.

So, basically, the Laws are created at the beginning of a Kalpa and they are fixed. Laws change depending on Yugas. And, Kali Yuga marks a state of complete disobedience to these Laws. So, in Kali Yuga a complete lawlessness will prevail not because there are no scriptures to be followed in this age and neither because scriptural laws have become invalid now but because people's nature is such that they won't simply follow scriptural injunctions.

Answer 2

Neither is the answer. Scripture does not have veto power for matters like customs and traditions that can be decided by reason. Vedas should be used only in matters which can not be probed by any scientific method or decided by human reason. Vedic authority does not extend to matters which can be decided by human reason. I am posting some quotes that will hopefully make things clear.

Bhishma said in Mahabharata Shanti Parva Section CXLII:

Even the words heard from an ignorant person, if in themselves they be fraught with sense, come to be regarded as pious and wise. In days of old, Usanas said unto the Daityas this truth, which should remove all doubts, that scriptures are no scriptures if they cannot stand the test of reason.

Mahabharata Shanti Parva Section CXLII

Acharya Shankara, for example, in his Gita Bhasya 18.66 says:

The appeal to the infallibility of the Vedic injunction is misconceived. The infallibility in question refers only to the unseen forces or apurva, and is admissible only in regards to matters not confined to the sphere of direct perceptions, etc ... Even a hundred statements of sruti to the effect that fire is cold and non-luminous won't prove valid. If it does make such a statement, its import will have to be interpreted differently. Otherwise, validity won't attach to it. Nothing in conflict with the means of valid cognition or with its own statements may be imputed to sruti.

REF: Srimad Bhagavad Gita Bhasya of Sri Sankaracarya translation by Dr. A. G. Krishna Warrier, p. 629.

Yoga Vasistha II.18 says:

yuktiyuktamupādeyaṃ vacanaṃ bālakādapi | anyattṛṇamiva tyājyamapyuktaṃ padmajanmanā || 3 ||

The remark of a child is to be accepted, if it is in accordance with reason; but the remark of even Brahma Himself, the creator of the world is to be rejected like a piece of straw if it does not accord with reason.

REF: Vasistha's Yoga translated by Swami Venkatesananda, p 35.

Sri Vachaspati Mishra, another Advaita Vedanta philosopher, says,

Na hy āgamāḥ sahasram api ghaṭam paṭayitum īṣate (Bhāmatī, Introduction)

A thousand scriptures cannot make a jar into a cloth.

Bhamati introduction by Sri Vachaspati Mishra