yes, the currently selected unit gets the benefit of the cheat. if you select a group of aircraft or double click a type of aircraft which selects all the aircraft of that type, only the one you selected will be affected. however if you click on each of them individually then they all get the infinite ammo. it should NOT affect enemy aircraft at all. go ahead and try it.
so you can:
activate cheat: select individual aircraft one at the time to make them inf. deactivate cheat:
or leave the cheat on at all times knowing that when you select any of your aircraft they will have endless bombs/missles. it's up to you.
once you select that aircraft with the cheat activated, it will remain that way even with the cheat off.
hope this info helps=
ps. i can probably make this option affect friendly tanks, walkers, etc. also. in other words all missle or large bore weapon shooters would have instant fill and reload. another option that may come out is a single keypress that makes ALL of your units invincible that can be turned on an off with one key. maybe in the next patch we add some more cool USEFUL options.
Hmm i'm actually getting interested in this trainer discussion. What does this trainer do? Alter the ammo to a "lots of nines" amount? If it actually alters the amount i suggest -1. That's a little thing i learnt with tiberian sun. I mod it. If it's more complicated, then i don't know. But at least i tried to be of any help xD