It is not possible without modding.

I usually try to get Coop as soon as I viably can.  Before then I build troops, yes, but more of the throwaway variety.  Once I get coop I then start to incorporate more crystal accessories and weapons.

Yeah sadly a lot of the older troops have to get disbanded or get guard duty because against tougher opponents they just don't have the attack power to make a dent.

Which isn't necessarily a bad thing.  Sometimes I get a bit of a scare when enemy units pop out of the FoW, then I see that they're going to attack a city with old, veteran units and I'm like, yeah good luck, have fun trying to take that city.

Well I'm not sure the soldiers on the ground would agree with arbitrary upgrades, 'specially if that new unit type is the other gender.  They might desert and run for the hills.

I think we should have the opportunity to increase 3-soldiers troop into 4-soldiers troop or more. Make the gildar cost higher with the troop's level, if you will, but please make this possible.