Yeah I fear it’s gonna be quite some headbutting to get it thought out, hence my original question.
Just saw that there’s some options for 5E like epic boons after level 20 based on experience, and ASI’s and feats extra based on experience.
Could just develop Advanced Beings stuff in a string of epic boons and ASI’s/Feats that require a certain amount of experience. That seems to be the simplest mechanical way of doing this.