I had a genius idea for the blanking plates...
Get some stong, (and i meen strong) araldite or sealant on the underside of it, if they try taking off the new one, it will break off and they'll have nothing to take, just a broken blanking plate!

the only downside is
1) not good if you need to take them off
2) might take some cleaning if they do take it again...
But at least you'll feel smug...