I don't recall any specific mileage actually being on the sheet, despite what the earlier post said. As far as that and the exhaust go, they never even looked at the bus. I don't think I even drove it that day! There doesn't seem to be any provision to physically inspect the vehicle initially or otherwise, and with it being a permanant tag, how are they going to check your mileage??? They'll never see you again. Remember the 63 panel shed with no engine? It got a tag! Moreover, I think they just want you to sign the form and your check so everyone's covered.
I've always had good luck with the downtown office when I've smiled, been friendly, played dumb, and let them ask the questions! I try not to say too much (is it okay that the exhaust's changed?) because then the clerk has to give an accurate answer that won't come back to bite her later. That's probably why they keep the questions to a minimum, too.
Good luck! It shouldn't be a problem!