[QUESTION] Adaptation the multiplayer missions for singleplayer

Up after one and a half hours...

i've personally never made a multiplayer conversion to singleplayer.

Do you mean what changes you have to make in the mission files? (actors.bin, scene2.bin, scripts)
Just have a look what changes been made of already converted missions, like Africa1(Airfield) e.g
Singleplayer missions can be downloaded on our Google Drive:
Hidden & Dangerous > HD2 > Custom Maps > Singleplayer

If you want to create a new mission without overwritting an existing one, would mean to edit Gamedata00.gdt resp. Gamedata01.gdt
Never tried, so don't know if and how it works