I'm trying to give my copy of the game an overhaul to more closely match the Lawrence Holland space flight sims (X Wing, TIE Fighter, Alliance, etc.) which are also available to play on GOG.com.

However, RebEd doesn't seem to work. It looks like this problem is well known to GOG.com, and it's more with the RebEd editor itself with its problems with modern versions of Windows. (I'm running Windows 10.)

I'm hoping to change the TIE Defender to an Assault Gunboat unit instead (if we're limited to just four fighters per side). Does anybody know of a preexisting Assault Gunboat card for this? Or has anybody gotten RebEd working with the later versions of Windows?

RebEd relies on registry entries to work. I posted a walkthrough solution, but can't link you to it, so you'll have to search my posts.

If you understand the registry, the problem children are DllLocation and TooBigLocation.