Ya know, the OP, or anyone else lettering re-paints are gonna do what they wanna do.
There are so many variables going on here, that I think most of us are saying..... to be safe....... wait. Getting something signed and then having an accident will still get that horrible reaction in the pit of your stomach, even if the owner says, no big deal. You still, as a professional, ruined someone else's equipment.
From not knowing what the paint shop really did as far as paint composition to baking it, to the owner saying give me a cheap job to maybe it wasn't prepped correctly or overspray is involved... so many conditions will make the final step fail or pass.
I saw years ago a guy in a shop where I was working using tape top and bottom for his flats on a baked on job. The truck was a large flatbed cement hauler with a huge crane on the back.
He started out by pouncing the copy and logo on both doors. Then he went back and put the tape on all the flats leaving the rounds open. He then lettered the first color on both doors. Went back to do the second color of the driver's door. When the second color was on both doors, he proceeded to take the tape off of the first color. Pulled the new paint off like it was meant to. He had, I believe it was red poking through a yellow-orangish new paint job. It looked horrible. I remember hearing the swearing and yelling and throwing chit around and knew instantly what had happened. After walking over, I knew why an old-timer had told me long ago, not to use tape as a crutch. Finish off your own letters and don't rely on tape. He'd always say something like real signpainters, don't use tape.
Many painters used the tape top and bottom method to speed things up, but it was really unsafe to to on re-paints. For the OP here, do as you see fit or are instructed to do, but make dead certain, you get those numbers on precisely where they're supposed to go, cause if you pull them to re-position them, you could very well be up that famous creek without the proverbial paddle.
