Ben:
There are two approaches, but both require some knowledge of GDL. The command that reads the Project North direction is
GLOB_NORTH_DIR.
1. Open an existing North indicator library part and search the 2D Script for where the 2D Symbol is drawn using GDL commands. Script your own North symbol, replacing the existing code. Some of the supplied GDL parts can be very complex, so searching and replacing code can be difficult.
2. Write your own object from scratch, using GDL commands to draw the symbol and rotating it using the GLOB_NORTH_DIR command.
If you search the forum there are links to guides about scripting in GDL. It takes some time to learn. Scripting from scratch on a relatively simple symbol (2D only, don't need to get into 3D) would be a good beginning project.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David