1) You can prevent the appearance of a week of creatures or a month of plague: this is achieved by connecting the SOD_SP plugin HD mod.
2) You can level up a hero using anything that gives experience: events, Pandora's boxes, seers, etc.
3) This can be done using the extended WOG/SOD map editor. Here is its standalone version. Unzip the archive into a separate folder (not in the folder with the installed game!) and run it from there (it is convenient to create a separate shortcut). When saving, remember to choose the file type "Heroes 3 SOD map file": by default, saving will be in the WOG map format.

I understand point 3 now) and indeed, there are additional properties there, although it is still limited. And regarding the SOD_SP plugin: can you only disable and edit things in the game, or also before the game? I mean, can you work with it like in a regular map generator? And does this mean that if you make changes this way, players without this mod will not be able to play? Thank you.
And another question arose: how do you make an enemy hero start moving at a specific moment? Does anyone have any ideas? I placed a passage guard, so that if I defeat someone, he will come out, but it doesn't work) he just stands there and doesn't even try to knock