yeh I noticed that its impossible to mod any of the maps - for example, I zlib decompressed nuked and changed some of the worldspawn settings like set the sunlight to low and direction as well but no matter what I do, the map is still exactly the same. I think its to do with the encryption because most of the file is still encrypted and all that you can get out of it is the *.map files.
I heard that someone extracted these *.map files and managed to load them up (with parts missing) in WaW Radiant - however, because the encryption is different, even if you mod it in Radiant, they won't be usable in black ops.