Yes its ok to paint your blades, a gentle sanding and a repaint...or even a varnish
It would be a good idea to re check the balance of them after painting.
You could even cover the blades with sticky backed vinyl...like they use for signs etc...I did this once but never got around to using them as I changed the helicopter for something a bit larger.
If you use the vinyl, make sure to leave the overlap at the trailing edge of the blades...and going 'with the flow' ie it cant get picked open but the air as the blade whizzes around...again do check the blades for balance.
As a note: if you ever have a blade strike the ground you should always strip the covering back and check the wood. Small amounts of damage around the tip and leading edge is ok...but only small amounts...like chips. Any cracks on the tip can be repaired with epoxy...or superglue...but we are talking small cracks.
Any cracks near the center and the blade root...break the blade in half and throw it away...its not worth the risk of doing a repair.
Carbon blades are all the rage, but wooden ones are cheaper...generally...and do just as good a job.
Rob