Bit of a diferent Ammo trigger

I'm trying to create an ammo system for my RPG. Instead of just the typical thing where your unit has a gun and can't attack unless it has ammo, i'm trying for 'All units are melee unless they have an item (ammo) wich makes all their attacks ranged as long as it has supply.'
I can't seem to figure this out. I tried using Orbs as a base, but I cant figure out how to make them make the unit ranged all the time instead of just on aerial attacks.
If anyone has any ideas on how to help i'd realy appreciate it. Thanks! <3

I have experiemented with such a system and had very little luck. Mostly because using things like orb abilities to enable/disable attacks is pretty buggy. The simplest posibility may be having two versions of the unit, one melee one ranged, and switching between them. however if you have many different unit types i'd imagine that could get quite cumbersome.

Yeah I realy didn't want to do it that way, since there's 4 races and 5 classes that adds up to 20 diferent units, meaning 40 in total if i did it that way. Not to mention the triggers themselves.