I think you've had pretty much the same answers here. But to be clear, it is illegal for a manufacturer to refuse a warranty claim on the basis that the service has not been done by a manufacturers own dealer franchise. That loophole was closed a few years ago. What they can do is refuse a warranty claim if non-recommended spares/parts have been fitted or the correct service intervals/procedures have not been followed.
Having said that, if you have had it dealer serviced its usually a faster and easier track to getting warranty items replaced simply because there's an extra check to be made for approving the claim if the work was done elsewhere. Also, the dealer you may want to use to do the work may refuse if you have not bought the bike from them in the first place. Its the dealer that sold you the bike that you have the sales contract with.
I service my own bikes because I really enjoy doing it and know what's actually been done rather than what the stamp says has been done. As an aside I have saved a fortune on BMW service prices. I agree with Scotty that you need to be careful what you take on as a start and also you should buy a few decent tools where necessary plus the manufacturers service manual. Do some research first and ask questions from others who have done it before.
