Teen spirit does not change anything in your system (registry - system files) except from its program folder. It doesn't not get associated with any of your media files. The only thing, the setup application does, is to copy the required files, create the icons and add a quick unistall option.

Actually, you don't need an installation (if you are an experienced user). You can download a plain files archive with all the required files and just extract them somewhere in your drive. Teen spirit will work happily.

The last function makes teen spirit also portable.