Thank you for pointing that out! Registration is required if you fly with the prop guards on or anything else that places the weight of the drone over the 250gm. Any additional weight one adds in any form to the drone may make it subject to FAA registration. New owners must bear this in mind as it is possible to have that new drone confiscated for violation of FAA rules.
So, new owners, please do yourself a favor and double check weight if you do any mods to your new bird! This includes perhaps a skin, as well.
Personal recommendation: What is it, $5? It won't kill you for a peace of mind!