Number Plate bulb change

One of my number plate bulbs has blown.
I presume the to replace the bulb, you need to take off the cover that's held in place with a single screw - is this correct ?

Reason for asking, is mine appears to have rusted and I don't wish to drill this out if it's the wrong thing to do.

Could someone advise please ?

I did consider removing the whole assemble - I unscrewed the two self tappers that hold it onto the bumper - but I cant see anyway of getting it off the car. Presume it comes out from inside the internal panel and you cant simply drop it down from outside?

Just an update (in case anyone else is interested).
Managed to pull both assemblies through the holes in the bumper. Both were very rusty and needed a desperate clean up.
Replaced both lamps from the rear side and left the covers in place - screws are so rusted you can no longer even see the Torx head !

I imagine that they could be a common or replaceable item, just not sure with what other car.