Question:
In the 2nd mission, it seems that you can only exchange red creatures for green ones in the fort, and for an additional fee. This is a bit annoying because troop summoning doesn't work in this case. And running back and forth with heroes to the fort every time is inconvenient. If I install "a mod that allows hiring these creatures in the city", will it work? Will I have to start the campaign over? Or can I continue from my last save?

Completed the 2nd mission more than six months ago. Pyrrhic victories over elves were simply tiring (you can't do without Darkness, luckily there's a mentor). Still haven't figured out how the fort works, and it's completely unclear how to complete the secondary quest (not fighting the dwarves). Is this a joke? Because you still have to defeat them, and the bonuses in the 3rd mission are given anyway. I regret not leveling up Varenik better. Moved on.

Here you can train ordinary improved creatures of the Order faction into soldiers of the Unicorn Empire. This requires gold: 10, 30, 45, 120, 250, 400, 700 gold per creature. The "Counterattack" and "Experienced Commander" skills reduce the retraining cost.
Click OK and drag the squads you want to convert into the top window.