Changing playable and viewable leagues in an existing save?

Is it possible? I'll go to any lengths to do it. The reason I'm asking is cause I'm pretty deep into the game, year 2035, and the game isn't running very fast anymore despite me having a perfectly good computer. I think it's because I have 12 leagues added, and all of them are playable.

I am madly in love with this save otherwise, have been at Man U for 5 seasons and don't wanna restart, but the loading times are starting to get to me.

It is not possible to chance it but I think we should have the option to remove leagues from the game.