[Imp]

You have some intresting ideas & present them fairly clearly.
Your aim here I think is to stop drawing fire mainly with more distant lower threat units.
keeping in mind this is a very old program near its limits perhaps something a bit simpler might work along the lines of.
Unit fired on always returns fire at firer.
Other units will check for other similar units at closer range if the firer is further than say 1/2 or 2/3rds max range from for infantry.
To some extent this does happen as unit will not take the shot with a low hit chance.
I have afeeling the way the game is set up you can't do what you are asking for it can only react to the current unit so your choices are to fire or not.
With this in mind buy the CD & when you need to set the op fire filter to restrict fire to the targets you want.

Your other option play a game that is not based on moving units individualy. It will play much slower & need very good AI routines to work well but if both sides give orders then press go the computer would then take over & try to carry them out.
So if you told a unit to move to here but it met enemy it would decide based on threat level what to do. Keep going, engage or withdraw.

The mechanics of single unit movement means this would need some careful thought as curing one evil will probably create a new one to exploit.