Questions about the Heroes 4 map editor.

if it's more than 10, then subtract 1 peasant.

You can simply check how many peasants appear.
We conduct the test as follows:
On the map, place a thief hero with 5th-level scouting (to observe the peasants) and 10 peasants.
Each day, we monitor and then determine how many peasants appeared and after how many days.