The lamps are set during manufacture and checked at the Dealer during PDI (or they should be).
The adjustment will alter the beam pattern and may make them illegal for use on UK roads at night if mis-aligned.
Additionally the performance will be affected if not set correctly, giving poor visibilty.
The beam pattern has a LH dip which you can adjust, but only position you can't remove it (hence the use of stickers to blank it off for driving in mainland Europe). If your not careful you'll need it set at the dealer after you've had a fiddle to get it set correctly.
HID lamps have auto levelling too so be careful not to over adjust the lens.
The simplest way is to add some tape to the outside of the light, not pretty but cheap and effective whilst remainlng legal in the UK and overseas.