I flashed rubix 2.0 and i want to use one of his themes as well. i have the file do i just flash ontop of the rubix rom? do i need to wipe anything first?
No, just make a nandroid backup before flashing the theme, restore it and flash another theme if you want. You can also try reflashing the ROM over what you have without wiping to remove the theme (possible bootloop situation) if it does loop, boot into stock recovery and wipe data and cache.