Is there a way to toggle whether or not specific DLC is enabled?
The way ME2 DLC is handled is rather poor. If you go into your mass effect 2 install folder, you will find a folder called BioGame.
Inside that, is a DLC folder with a bunch of sub-directories for each DLC.
To 'disable' DLCs, you have to move the particular DLC inside that folder out, or delete it.
This is for the entire game, there is no way to do it per character.