It is possible, and is relitively simple. Howver if your painting them with the tyres on the you have to spend some time masking them up properly otherwise it will look rubbish. Its mutch the same as paining any pannel. Rub the surface down to give the paint something to key to, then spray with your desired colour. Complete a few coats, rubbing down with some wet n dry sand papper in between every few coats. Then finish it off with a few coats of laquer (depending what paint your using).
For oktopod, that too is possible, although its a little bit more of an involved process. You do mutch the same, but youl need a "candy" paint. Depending on how much you want your alloys to "bling", you may need to lay down a bright undercoat like white first.
All of the above is best done with tyres and valves off!!