GPS/Compass rotation

I have a Pixhawk with an external GPS/Compass and I only want to change the external compass orientation (180). Is it possible? I think I should use COMPASS_ORIENT=4
So my idea is Pixhawk arrow forward in the direction of the plane, and GPS/Compass arrow backward.
Or If I use COMPASS_ORIENT=4, do I have to rotate Pixhawk and Compass?

Dear Community

No matter what I do I get compasses inconsistent. I would like to ask you the orientation of external compass ( HMC5883L) . My opinion just Rotation_180 ( Because compass is upside down).

Schematics Here