Unfortunately when I attached the Stephanie plates about four years ago I used a rather strong silicone adhesive. It was a bit of a struggle to remove the plates. I had to lever them off with the aid of a screwdriver. The tank sides of the loco are made of wood and I could not avoid denting the surface in my attempt to remove the plates.
Once the plates were off, I set about filling the dents with Milliput filler and then sanding the filled areas back to a smooth surface. The affected area was then given a coat of gloss black enamel paint to match the rest of the loco body. Once the paint was dry, the number and name plates were fixed in place with a very thin smear of silicone adhesive.