HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

So, someone who is on your blacklist cannot join your game anyway.
When they try to join, your game will simply disappear from their list.

Also, you won't see the games of those who are on your blacklist.

This is how it is and how it always was.

I will add asterisks to the password of the created game.
I will also do something about the numpad. Numpad functionality was a feature of HW rules. This functionality conflicted with something in HD, and I disabled it when I integrated the HW rules into HD...