Is it possible to edit a random scenario to eliminate certain subformations?

[JWW]

I was playing around with editing a random scenario to see if I could easily create a 1900 era random scenario with just some basic starting SF (meaning submformations), primarily the ones you can get if you uncheck full first level tech, but without trucks. The key word is EASILY. I found out how to disable research and how to add SF to the starting available SF. That is pretty easy. But I don't see an easy way to eliminate trucks (or any other SF) from the starting available SF. Is there an easy way to do that w/o creating a new masterfile, which I don't plan on doing? Basically I want to create random scenarios with the starting infantry type units and was going to add perhaps infantry guns and/or artillery and use horses as my only transport means and with no research available.

[JWW]

To answer my own question, I don't think it is possible to edit a random scenario to eliminate trucks.  I could be wrong on that.
 
But I took another look at creating a modified masterfile and realized it was not as hard as I thought.  In about 15 minutes, after one miscue, I was able to create a modified masterfile to allow me to play random scenarios with a 1900 style subformation list (at least my version of such a list).  I included horses, rifles, engineers, staff, infantry guns, mortars, and artillery.  There is no research so you play with what you have. 
 
The small random scenario I played turned into a battle of attrition with continuous static front lines after an initial maneuver phase, and I won in a slugfest mainly because I happened to have a better starting position than the AI.