I am pretty sure you can initialize (re-intrialize) your M400 as a MARATRAC.
I ran both RSS, M400 and MARATRAC, just now and I didn't see a choice for changing the control head setting.
So I am pretty sure you have to blank and re-initialize a radio to change it's control head config choice.
As I recall, I used MAXTRAC LAB to BLANK the logic board.
Then ran MARATRAC RSS to initialize the radio and made it an A2, A3 or A5 as needed. (or A7 of course)
Rotary head A2 being 8 Ch with repeat / direct , 3 being 16 ch with SCAN.
Going from memory here.
You will absolutely need an old 286 or 386 or 386 SX to get those two programs to run AND to program a radio.
Many have tried, and some claim success, but I have never gotten a newer computer to run AND program a couple of
these old RSS programs.
I will look for some A5 files, but I am a few computers beyond having an A5, so might not find a file.