Please no cease and desist, please no cease and desist……
Fallout
All things about Fallout series.
I don't know if it uses any assets from Fallout 2, but if so, the Tale of Two Worlds mod makes use of Fallout 3 and Fallout: New Vegas assets, and Bethesda's obviously okay with that. It, IIRC, requires that both Fallout 3 and Fallout: New Vegas be installed, so I imagine that that route would always be available, even if Bethesda isn't okay with this as it stands.
You can always legally distribute a set of non-derived-work changes to a copyrighted work. End users can apply your changes to their own copy of a copyrighted work to create a derived work from a copyrighted work. This is true even if it's not legal for them to then subsequently redistribute the derived work -- copyright law doesn't prohibit creation of a derived work, just distribution of same.
Tale of Two Wastelands, in case anyone read your comment, was inerested, but couldn't find anything.
Wastelands
Thanks, yes.
TTW needs an installed copy of Fallout 3 to rip assets from (it's a New Vegas mod).