as long as the theme is ported for Kang, you can just flash another theme over the existing rom. it will just replace the theme you are currently using, but won't affect the rom. don't need to wipe, either...
altho, you might want to consider updating to LithMod (it's updated version of Kanger 5.0.9)...
i just looked, and it does appear that each version is a full rom. regardless, even tho you are switching roms, because you are just going from one Kang version to another, you shouldn't have to wipe...