Current questions and answers regarding the map editor.

If you change the name of the portal, it will remain a two-way portal.

Added after 48 seconds
How do you create a monster on the map that always joins your side for gold and no other way, neither for free nor by fighting?

Added after 3 hours 41 minutes

How do you change the amount of gold a mine gives per turn?

And how do you change the size of an already created map?

Study the basic scripting manuals, and then the answers to your questions will come to you on their own: Ogo-I's scripting manual for beginners, the Heroes 5: Scripts (3.1, 3.2, 3.3) video on the Heroes for fan channel, JackOfShadows' FAQ.

I will only answer the last question: it is not possible to change the size of a created map.

Azgalor, floor and ceil are mathematical functions for rounding down and up for fractional numbers