So, I'm making a custom career mod, and I'm not entirely sure how to test it with only the basegame/certain ep combos. Is there a way to do this with a program, or do I have to completely uninstall my eps? I really don't want to do that, so if anyone knows of a program, or is willing to test the mod with just the basegame or certain eps, the help would be really appreciated! :D

Hello !
Okay so I'm not sure this is the best of ideas, but that's what I am doing.
I have 2 The Sims 3 Folders (the Program Files one). One of them is the one I use to play it contains all those other folders : The Sims 3, The Sims 3 Ambition etc...
The other one only contains The Sims 3.
Before I launch the binary for the game, (not the 1st of course), I move all my saved games and other heavy files to another directory so that the game takes less time to load.
Then, all you need to do is create a simple game, in a simple base game empty map (there are lots of empty maps in the Sims 3 maps download section) and create 1 family, with as much sims as you need for your tests. This way, its takes less time to load between each tests, and you know your mod works on a base game setting.

Don't forget to swap back your saved games before you play.
Alternatively, you can add ".off" at the end of your saved games folders.

Please correct me if there is a better way to do it, I would love to learn as well.

It is very easy to set up different combinations of EPs using Any Game Starter

Or... this.