I do not recommend painting your racket, mainly because of the weight factor. You might unbalance the weight of the racket and it will mess up your play.
It could probably be done (loads of people have done it to tennis rackets). There is a guide on the Tennis forum - it should answer most of your questions plus there's a step by step guide on how to paint your racket. I see no reason why the techniques described couldn't be applied to a badminton racket. I'd definitely try it on an old racket first though.
