Just disable save at the start of the game, and if there's ever a point where you WANT the player to be able to save via the menu, enable it again. The save crystals example shows you how to force a save when it's disabled via the menu. Not sure what "event the whole map" means - when you disable save, it's disabled permanently until you say otherwise.
Anyway, you should have what you need now, so This thread is being closed, due to being solved. If for some reason you would like this thread re-opened, please report this post and leave a message why. Thank you.