It's off by default.
If he's using something like EAH to manage his server he'd change it in there. Otherwise in an already running save game he would carefully edit the gameoptions.yaml file found under his save game, or if he hasn't started the save yet he'd edit the gameoptions file inside the scenario itself before starting a new save game.

A note about editing that file is it's very very picky on formatting so he'll have to look it up and do it right otherwise the game will revert to the games defaults for all settings.

You'll know it worked if you can't place a core on most POIs.

Thank you for the response, we have already started this save, so I'll look in their files with them / back it up / edit it.

I do see it in the scenarios workshop files gameoptions.ymal, I didn't think to look there.

The reason I posted is because at the time when I was searching around I only had my own RE2 singeplayer save file gameoptions.ymal to look at, and I didn't see anything about RegeneratePOIs in those saves.

I'm guessing the multiplayer file has more options that can be changed than the singleplayer one.

Thanks again.