To make your own mission you have to write a .DLL file which specifies mission settings, unit placement, etc. This requires some C++ knowledge.
Make copies of the text files instead of putting them back into the VOL. If there are text files just sitting in the game folder those will be read instead of the VOL ones.
Also, be sure you or your text editor doesn't change any tabs to spaces. (Use a plaintext editor such as notepad, never a word processor like MS Word to edit these files).