And post a link to it here, please and thank you. 
I’ve seen several of them while searching the forum for instructions. Here’s one such example, I believe there are a few more in that thread, along with a handful more in their own threads. Mainly people are trying to alter the colour and size/placement of the license plate text for the purpose of having another state/country’s plates. Some even want to make ‘add-on’ plates and go past the default amount of plates. All this is possible via carcols.ymt to my knowledge.