FOSS gamedev and creative worlds

can a mod be made to set up zones where people can damage others and where they can not?

Kinda like the wilderness from runecraft. enter the zone anyone can be hurt. outside the zone you cant hurt anyone even if you tried.

If so can it also be applied to where mobs can populate or not? have a zombie area or a zombie free area.
------ This one i think will be more modifying the mod that already exists and add setting for a pop area for them.

How about, use the players onstep to check if they are in a safe zone. If they are, then reset their health to full each step.

You have to write code to make mobs spawn, so just ensure that when spawning one it's outside the safe zone, if not then just don't spawn it.