You can leave the kit in place but you will have to disconnect the ballast. The ballast connects to the original bulb connector so you disconnect that, remove the burner, put normal bulb in and reconnect the original connector. You will also need a grommet to fill the hole that is left when you remove the burner. It's pretty simple when you see it.
By the way your unlikely to fail an MOT with it but I know some eu countries don't like them.