HL2DM mod?

I want to make a mod for HL2DM, starting with the already existing HL2DM, not from scratch.

I make modifications to a HL2 mod (but limited to SP), and tried to
launch it with applaunch 320 instead of 220. HL2DM is actually
launched, but it doesn't use my mod dll, so my modifications are not
used.

Another point is it doesn't use my mod directory, but the HL2DM
directory. The proof is my map, located in my mod map's directory, is
not found when my mod is launched with applaunch 320. If i put my map
in the HL2DM map's directory, it finds it.

I tried too to change the gameinfo.txt of my mod, making it read SteamAppId 320 instead of 220. No result.

If anyone knows how to do this, please help me, I don't want to create
everything from scratch, models, sounds, textures and so on. Perhaps
later, but not for now.

Pleaaaase !

What's the problem? I think, if you need to modify something, just
extract from the gcfs the files you need to modify and place them
in the folders(hl2dm folders or sourcemods/ to make a separate mod)

Starting from scratch means rebuilding the source binaries, not models and textures ecc...