Well, funny story, i just did that. But my PSB towers are a little long in the tooth and i was tired of the black ash vinyl finish. I veneered the B&W sub as well, and its teeth were not so old. Now they are piano black and hand-rubbed mahogany real wood veneer. I like them much better now and the WAF went way up. So, in short, it can be done. But you better plan ahead.
Sanding and painting perfectly good speakers

Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire