Hello. 
Any suggestions? They really would make cool maps.
Just open the map with the éditor, delete what is not in tremulous (items like armours, medikit, weapons...), add an egg and a telenode.
Compile it again, test it ...
GTKRadiant can only open .map files, and all compiled maps are some other format--trem and q3(?) use .bsp
To do what you are suggesting, you would have to obtain it and the textures, decompile it, remove item spawns, add bases, retexture as necessary, THEN recompile. AND to decompile right would require knowledge of the original compile settings, as well as the game of origin.