Well stretching the frame for one, and most "full race " exhausts (which includes headers) are normally illegal for road use anyway, just don't hear about riders ever getting done for it, tail tidies etc are all illegal and will warrent a fine if the police officer wants (you can buy them from all bike shops and even when you buy new they will try to onsell it onto you etc)
I'm not having ago at you Zowie, but for someone to say that theres ʞ©$ɟ all regs for bike is insane.