At this point, I would say that pregmod is more like a complete rewrite. It is not just about the dozens new features (that's the tip of the iceberg), but also about how the code has been cleaned up and reorganized. I don't know if you have looked at the source code recently, but many Twine/Sugarcube parts have been rewritten in a more modular way as Javascript functions.
Regarding making it 18+, I agree that the right way to ask would be to raise a ticket with the staff. However, I have some doubts that it would be an easy patch because you need to do more than restricting the range of a few variables: the code and the story text have explicit references to things that are against the F95 rules. You will also need to modify these, and keep on maintaining your fork of the pregmod code base if you want to keep your version up-to-date.
I am not saying that it is impossible, but it is probably much more work than you think. The current maintainers of the code have stated that they have no interest in adding any censorship in the pregmod code, so you will be on your own if you want to release this and still stay up-to-date compared to the pregmod code that is in constant development.