Is it obligatory to renew the marriage contract after repeatedly committing the sin (anal intercourse) before the legal contract, and then after it? What is the religious ruling on this act, and does it invalidate the contract?

Anal intercourse is forbidden and a major sin; indeed, it is considered adultery (zina) necessitating a prescribed punishment (hadd) by many scholars, for an adulterer is one who commits an abominable act, whether vaginally or anally. It is not permissible to marry a woman with whom one has committed adultery unless she repents. However, it is permissible to act upon the opinion of those who validate such a marriage if renewing the contract would lead to harm. Repentance erases what came before it, and it involves ceasing the sin, regretting it, resolving never to return to it, and concealing one's own sin.