I would like to request that you create a new flag that allows specific block exceptions to the 'prevent-place' flag.
So for example. I would like a grief revert block that is placed in a 'message board' area. I dont want them to be able to place anything else in the area, except for signs. Likewise be able to delete (their) signs from the same area.

Another example is a 'wheat farm machine'. I would like it if they could replant the fields. This would of course be used in conjunction with the dont trample wheat flag thing you recently added so they they dont have to replow it as well.

I assume it would be best to be a prevent-place/destroy exception list rather than limit to one. But yeah. That would be hugely helpful.