Is there a way to play without the game adding the registry entries required for the game to "see" a CD? I'd like to travel with this game without having to install it on every computer or edit the registry like I can with other GOG games.

If this is something that is unchangeable, I'll understand.

I am also experiencing this error, I had it working but then reinstalled Windows. Since then I'm getting this error even after multiple reinstalls of Rebellion. I am doing more troubleshooting and will share any progress I've made.

Couple ??s
Are you running it in capability mode?
How was the install done (copy paste, download, or other?
Are you using the out of the box EXE or shortcut?
on the COG download the EXE ties to the reg entries in a wierd way and several I have dealt with just required a EXE edit Try this the new EXE from here doesn't call for a CD but the one from COG shouldn't either but if its coming from the original release on the download they may have not caught the error in it. Try it and let me know what the path is on your ex e now?
http://www.gamefaqs.com/boards/198776-star-wars-rebellion/63008006

Maybe more hits here.
I have the same problem where the game suddently asks for a cd.
I only use the GoG version (I use an Asus Transformer T100, no cd).
It does not matter if I use the desktop shortcut, the launcher or the rebexe file. I put everything on compatibility with win98 and run as admin.
I wiped the registry of any rebellion entries and reinstalled to no avail.