Custom Config Plates don't Carry over to the next time I spawn

I made an amazing sunburst police car with a carbon hood and other parts (no mods) and I put a Maine plate on it and put LOWE for my officer Deputy Lowe, but when I respawned it, the plate had a normal 6 digit non-custom ID, do the plates save in the custom config?

 

thank you! I wanted to also know how to make a custom paint job on a macbook, I play on my PC but have all the files stored on a hard drive that can only be accessed by a mac.