The licence plate is currently a decal of a Nova Scotia Canada plate.

This can be changed by these simple steps.

File is located in the decals folder in the mod zip.  The file is called: plate.dds

This file can be opened, you can either unzip/edit/zip, or edit the file without unzipping by using a program such as 7zip.  Keep a backup just in case.

To edit the graphic, I would recommend using paint.net

Try to match any replacement image to the same aspect ratio.

When saving, be sure to save as a .dds file, and keep all default settings... eg: DXT3 (Explicit Alpha)