I seem to do this a lot - I’ll find a game whose setting I really like, but dislike the ruleset it uses, so I end up converting it over to the ruleset I prefer (usually Cypher System). I’ve learned that to some people, this is blasphemy of the highest order, which is surprising. I still do it, though. 😬
Not what you are talking about but one reason I learned to love the champions system from the early 90’s was a guy there ran a fantasy setting using it. He had a program to he made himself to do the heavy lifting but the variable power pool rules gave him a great ability to have characters have any spell they wanted by talking to him. Just had to fit within the pool which as a magic user would level as points were put in.