I've swapped my normal sized number plates for the slim ones. The problem I have now is the large and ugly plate mounting brackets. So I'm looking at removing the brackets entirely and screwing the plate directly into the bumper. This would probably require drilling new holes through the bumper (though I haven't had a look under the brackets yet to see what is under there). Is there any downside to doing it this way?
Alternatively I guess I could cut down those mounting brackets to be slightly smaller than the plate.
Thoughts? Alternatives?

Remove the black brackets fully(will require drilling out rivnuts) then double sided tape plate to bumper

Thanks for the reply. I'd seen the 3M VHB tape mentioned in other forums. I'd have constant anxiety about the plate falling off, even though it is very strong tape. Or some toerag yanking it off.
Drilling out rivnuts sounds like a bit of a pain too. I may end up just cutting the black brackets down to size.