I thought the game writes entries into the registry? I may be wrong, but I thought it did. I don't think you can do this with out reinstalling, but I am not 100% sure.
It does. The problem is, seeing as my registry no longer points to the games, I've had to use a work around that EA left in the game, the Sims2.ini file. To clarify, everything added by expansion pack works. It's just the stuff pack content that's borked.
Anyway, I have an idea: the game might not recognize the spXdir format, so if I rename sp1dir and sp2dir to something like ep8dir and ep9dir, then it might work.
EDIT: OK, this worked, but I am now playing some sort of hybrid game which identifies itself as "Sims2EP4.exe" and "The Sims 2 Pets" to task manager, but displays the UI of Glamour Life, see below. I think I know how to fix this one, but the effect is weird.