Well, apparently TED5 can edit those maps and is open source:
http://www.shikadi.net/moddingwiki/TED5. It requires dosbox, not sure how easy it is to use.
If you are interested in improved open source tools, you should get in touch with the folks at
http://www.shikadi.net/Main_Page, I'm sure that they'd be interested in for example a Wolf3D editor for Camoto.
If you want to extend the game with new map features, my advice (from doing the same with C-Dogs SDL) is to use the latest/greatest from the ground up, for example consider writing plugins for Tiled to export maps, add spritesheet support and so on.