Configuration via Windows GPO -> exclude second Firefox installation

Hi, we want to switch our Firefox configuration from file-based (policies.json) to GPO-based. We rolled out the GPO on some test clients and it worked like a charm. But... It shows that there are some clients which need a second firefox installation for a special purpose, which is not allowed to enter the internet or update itself. The file-base configuration can handle these to different installations with two differend policies.json files. Is there a way to accomplish this scenario with the use of GPOs? The GPO-base configuration seems to be global for every client. At this moment i don't see a solution for our problem. Do you see one?