Its not against the warranty rules to have work done at another garage, but it is against the law if the issuer of the warranty tries to void it due to work being done elsewhere. Of cours it needs to be proper garage and not "John down the road"
First thing I did when I got my RX450H last year was replace the rusty locking wheel nuts, how a premium car manufacturer sends cars out like this is beyond comprehension
Why not just take the feeds from the overhead lights, there will be a feed for the sunroof that would be suitable. I did this on my Jaguar XF with no issues
Had one fitted to my gen3 yesterday but I've had to wait nearly 5 weeks due to delay in manufacturing, try PF Jones website and put your reg in, if Lexus do it Westfillia will also have an option