At present, no.
If a particular armor, robe, hood, hat or helmet isn't to your liking, your options are either hiding its appearance entirely which instead makes your character display in their camp clothes - Some of which are quite nice, too! - Alternatively, you can dye clothing, armor, hats, helms, bracers, boots, underwear and cloaks with the various dyes you can find in the world or on certain vendors to alter their coloring.
I don't believe Larian have given any indication of implementing a system to allow you to swap existing appearances and doing so would almost certainly require some UI work.
It's not beyond the realms of possibility for an official update, but it isn't likely.
