NOTE - Your question is not totally clear to me , but i am giving the explanation of Shree-Krishna marring 16,000 princesses here.
• Why Lord Krishna Didn't Break the Rule to give Dharma to the 16000 princess ?
The answer of your question and the clarification of Shree-Krishna Marring 16,000 princesses at a time is given in Shreemad-Bhagvat purana. SB 10.59: The Killing of the Demon Naraka. SB 10.59
So From the story we know that shree-Krishna killed Narakasura / Bhaumāsura and librated 16,000 princess , whom he abducted and kept in his palace. We also can see that , when all these princesses saw Shree-Krishna they got enchanted /attracted towards him and in mind assumed him as husband.
So it was the wish of all the princesses to become wife of Shree-Krishna . Knowing their wish Shree-Krishna , Assuming each separate individual form for everyone of them , and then married them.
तत्र रज्कन्यानां षटसहस्स्रधिकायुतम् |
राजभ्यो ददृशे हरि: ||33||
tatra rājanya-kanyānāṁ ṣaṭ-sahasrādhikāyutam
vikramya rājabhyo dadṛśe hariḥ
There Lord Kṛṣṇa saw sixteen thousand royal maidens, whom Bhauma had
taken by force from various kings.SB 10.59.33
तं प्रविष्ठं स्त्रियो विक्ष्य नरवीरं विमोहिता: |
वव्रिरेsष्टम पतिं दैवोपसादितम् ||34||
tam praviṣṭaṁ striyo vīkṣya nara-varyaṁ vimohitāḥ
’bhīṣṭaṁ patiṁ daivopasāditam
The women became enchanted when they saw that most excellent of males
enter. In their minds they each accepted Him, who had been brought
there by destiny, as their chosen husband.SB 10.59.34
भूयात् पतिरयं मह्यं धाता तदनुमोदताम् |
इति सर्वा: पृथक् कृष्णे
भावेन ह्यदयं दधु: ||
bhūyāt patir ayaṁ mahyaṁ dhātā tad anumodatām
iti sarvāḥ pṛthak
kṛṣṇe bhāvena hṛdayaṁ dadhuḥ
With the thought “May providence grant that this man become my
husband,” each and every princess absorbed her heart in
contemplation of Kṛṣṇa.SB 10.59.35
अथो मुहूर्त एकस्मिन् नानागरेषु ता: स्त्रिय: |
atho muhūrta ekasmin nānāgāreṣu tāḥ striyaḥ
Then the imperishable Supreme Personality, assuming a separate form
for each bride, duly married all the princesses simultaneously, each
in her own palace.SB 10.56.42
This is further confirmed in another chapter no 69 canto 10
चित्रं बतैतदेकेन वपुषा युगपत् पृथक् |
स्त्रिय एक उदावहत ||2||
citraṁ bataitad ekena vapuṣā yugapat pṛthak
dvy-aṣṭa-sāhasraṁ striya eka udāvahat
He thought, “It is quite amazing that in a single body Lord Kṛṣṇa
simultaneously married sixteen thousand women, each in a separate
palace.” SB 10.69.2
Conclusion - So marring to all these 16 ,000 princes abducted by Narakasura , was just one of the Leela’ of Shree Krishna. He assumed separate form as a husband for each one of these 16,000 princesses , and married them and carried the Ghrustha-Ashrama separately with wach one of them.
So he did not broke any rule , or nor by this act was done Adharma by marring all those 16,000 princesses .
Why didn't Lord Krishna Change that rule and allow to marry such women instead of marrying them himself ?
So the answer is provided by Harivamsha Purana. Where its said that those 16,000 women were Daughters of Gandharvas , and Seven different classes of Apsaras.
And some he also abducted some women. So they were devine women.
They were kept in separate city called “Alaka” on Maniparvata. And they were observing Sati –Vrata.) (faithful wife) So they were already pure even staying at palace of Narakasura.
So there was no need for Shree-Krishna to change the rule , cause they were pure and observing the vow of faithful wife (sati).
गन्धर्वाणां च या: कन्या जहार नरको बलि |
सप्त चाप्सरसां गणा: || HP 2.63.12 ||
gandharvANAM cha yAH kanyA jahAra narako balI |
devamanuShyANaM sapta chApsarasAM gaNAH ||2-63-12||
The Narkasura/Bhaumasura abducted many girls of Gandharvas , some
of them also were daughters of human beings , and some of them were
from seven different classes of Apsaras.
चतुर्दश सहस्राणि एकविंशच्छतानि च |
ekaviMshachChatAni cha |
ekaveNIdharAH sarvAH satImArgamanuvratAH
They were fourteen thousand and twentyone hundred women in all. All
were with single plait of hair and observing the vow of faithful
wife (sati). HVP 2.63.12-13