Locking Pieces on layer?

Working on a mod for Last Night on Earth. I have the map board pieces that I place to define the play surface. After the boards are placed, I need to lock them into place.

Is there a way to lock a layer (or all pieces on a layer) AFTER they have been added to a map board?

Ended up doing this with a “Replace with other” to change it to a copy of the same item with Does not stack set to disallow movement.