I haven't been on the Radiance, but let me give you my experience on the Breeze earlier this month.
We brought some Magnetic backed decorations (bought on Amazon) but they weren't strong enough to stick to the doors. They would stick to the walls both inside and outside the cabin, but not the actual door. I assume that the door design that makes the exterior look like slatted wood impedes the magnets a bit (unless they are strong magnets).
During our cruise as I passed by any cabin door that was decorated, I looked to see what was used to hold the decorations. I saw a lot of glue dots and tape. I also saw a few that had actual magnets holding the decorations on and they did stick but they were bigger magnets about 1/2" thick, not just thin magnetic backing like on the decorations I bought.
So anyway, based on my experience, depending on the what you are bringing to decorate with, I'd be sure to bring some non residue tape or glue dots as well just to be safe.