You can sand it down by hand using very fine grit paper for metal. You could then use a cutting compound with a polishing wheel to further polish the metal. I would recommend spraying the bare metal with a clear coat to protect it from staining or marring the bare metal.
Yes you can paint the covers, read my prior post.
In the previous post you stated "even the camera lens", don't paint the camera lens. Camera won't work then. Camera bezel ring is ok to paint, just not the lens! If you paint the speaker grilles be careful to not obscure the holes in them. Very, very light coats on them. Always let paint dry between coats, or the bottom coats will NEVER dry.
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