Pa has vanity plates and only recently allowed YOM plates. Maybe 20 years ago I had a 1939 plate restored for my 1939 PU truck. I wanted to use it so I drove to Harrisburg right to DMV head quarters. I took the plate along and I asked the nice girl at the counter if that particular number was active. A few clicks on the key board and she said no. I said "OK i want to register my 1939 truck and use that plate. She said I couldn't do that. I asked why not it's a PA plate with an open number. She said she didn't know why not. I asked her if she could find out why not, it's a PA plate after all. She said "be right back" took the plate and left. Came back shortly and said "Wrong material, wrong color, and non reflective.............. Case closed.
So I asked if that particular number was assigned to a vanity plate. She looked at me sweetly and said "don't even think about it."
So..........I bought a regular plate, put it in the glove box, put the YOM plate on the truck and I've been using it ever since.
Plan "c" if I'm ever stopped I'll claim I'm old and confused and just came from a show and forgot to put the real one back on.
" I'll do that right now officer. Thank you for pointing that out."
It should work, I think...............Bob