I sorry to sound stupid but can you just say that again...?
your looking to import a bike or is the bike already here...? ad you wanna buy that...?
If it's got a full registration for the UK what's the problem...? it'll have a certificate of conformaty an MOT and whatever tax was or may have been due would have been paid. In Japan they drive on the same side as here, the clocks will be in KM's so a sticker will solve that problem... to get the MOT, the headlight will be fine, indicators will be yellow.... afterall Japan is a civilised country, they don't cause much harm (anymore)
Why would you be partexing a bike you've just bought...? sell it privately...? solves that I guess... or the dealer will make an offer, so they don't loose out if your part exing it?!? As far as I know they don't build BMW's in japan so I can't see it not being under coated properly.... which japanese imported cars suffer with... (uk cars are different) perhaps you might wanna delete the question and start again.
follow the simple pattern
what, where, when, how, who and why...