Options: 1) A talkbox that simulates the recruitment window, specifically with + and - buttons. 2) Hide a garrison on the map so that no one can see it. When touching the recruitment building (with its standard property disabled), fill the garrison only with creatures that can be purchased with "gold" or "leadership" (here, authority). It's better to do it one by one (by type), as you'll have to make additional checks. Then, force the hero to visit this garrison using scripts. 3) Reset the dwelling's values at the beginning of the week and after touching it. When touched, determine what type of dwelling it is, and change its growth rate via scripts to the maximum possible based on authority and gold. This only works for dwellings where you can recruit an army of one type.

Added 7 minutes later

Options:
Also, when upgrading creatures or taking them from a garrison, the change in available authority is not taken into account, so the hero can gather an army larger than what his authority allows.

1) You can run a constant loop and check the quantity. 2) When touching the garrison, reduce the army in it to the extent that the authority allows. And make the upgrade/no upgrade option with a single authority value.