AZCoder released his AZC GPS Replacement Mod on the BI forums.

Quote AZCoder :
This is a simple addon to replace the default GPS UI with one of five others as shown above. The first image is to give an idea of what it looks like in full screen mode. Comes with a userconfig file which determines which image to use, simply uncomment the one that you want to try and comment out the others. Of course you need to reload the game each time.

Since this is a client-side mod, as far as I know it should work in SP or MP with no effect on anything else. Let me know if that's not true, or if it causes any problems. This is my first non-campaign addon.