A couple of years ago, when we were still contemplating the new paint job -- I requested and received a "spare" 175 sticker for my bike. I knew the old one wouldn't survive being removed from old bodywork. I got it at the registration trailer during an event - by showing a timing slip where I exceeded the 175 in the quarter. The timing slip, of course, showed my bike number -- and that was all there was to it.
Of course, maybe I'm a little more anal-retentive than the next racer -- but I had the sticker when I needed it.