Any change is possible if you put in the time and effort.
The flavor text provided during sexual interactions is created by ".../files/scripts/sexdescriptions.gd". The system converts pronoun tags into the most specific generalization for the group. Though it was designed for a simpler conception of pronouns, it should be relatively easy to adapt if you have already managed the change in person.gd.
The core of the sex interactions is ".../files/scripts/newsexsystem.gd". Search the file for the trait name. You will probably need to add exceptions for the action codes for those actions since the original system was designed with phallic-based assumptions about which side was the "giver" or "taker".