Ok, so I'm rocking along with my level 9 units on my main exploration champ's army, with three units per army, and now I've researched the tech that gives me squads. Is there any way to upgrade 3 unit bowmen to 4 unit bowmen? Or am I stuck with training a new green set of troops (maybe + a few levels if trained from my fortress town), hoping they survive enough skirmishes with monsters to be viable vs the other sovereigns?

I ask this because late game, with Gildar, I spit out a few Iron Golems with a number of max squad size archers and mages and now I have a Deadly class party of 6 level 4 base units. This is against my Deadly 9 unit sovereign army with level 8-11 units of 3 or 4 stack size dropping back down to Strong if I happen to lose one of my grunt units in a battle vs Fire Lord's many calderas.