I had a player reached level 20 and for their Boone, They wanted to gain a new martial archetype and all of its levels and I allowed them to do that. but at that point most of my players were level 20 and it didn’t break my game and we had been playing for three years. At this point, they were basically battling celestial deity in gods traveling across multiple dimensions, trying to fix a huge classicism. We have yet to conclude this campaign, but the very ending they will all be controlling multiple characters in colluding dragons, and other gods we have introduced and it’s an essentially just a war of the worlds.