I can't speak from experience for the rim-side of things, but everyone i know of that severely overheated their engines with aluminum heads ended up replacing the heads (not always immediately) due to them being too soft to hold a shape. Most ended up eating head gaskets since they won't seal quite properly anymore.
I'm imagining the same thing can easily happen to aluminum at temps required for powdercoat.
Your mileage may vary, though, and I'm not a metallurgist/etc, I just have seen these things happen
