I don't know why you don't want to reinstall impulse but if you do, you will not have to redownload games.
Also you coud try remove settings in registery (may Break some things):
Also there are some xml files in:
Document and Settings/'YOUR ACCOUNT NAME'/AppData/Roaming/Stardock. (This are hidden folders and Folder Document And Settings in Win7 is called Users)
Document And Settings/All Users/Stardock
But i still recomend reinstall