I have had a browse through previous posts and didn't manage to find my answer
Do PUs effect spells per day?
What sort of upgrade are they?
Are they like a band from Pathfinder or more like a Manuel?
I've always run them as the upgraded ability score is in all ways your new ability score like the manual/wish from pathfinder 1e. Sure you could technically uninstall an INT upgrade and have to figure out what you had spent those skills on, but that has never come up in play for me.