Had a couple of strange experiences with modifications.
Way back in 1980(?) when the OE tyres on the Z-400 wore out replaced them with Avon Roadrunners. Declared it on my insurance renewal - the one time I have been refused insurance!
Fast forward to 2014 or so. My 2nd ZX-9R was basically a track bike on the road. When it was rear ended at a roundabout, got it home. Was not looking forward to the assessor turning up...I won't list the changes to standard here, but there were a lot.
When he did, he confessed he usually dealt with cars. The only non standard item he noticed was the paintjob!