If you use a flux-gate (heading sensor) to keep your chart/radar oriented to the bow of your boat or for your auto-pilot, I suppose over time the calibration could change. If/when that happens, you'd just need to go through the calibration dance. My Garmin MFD lets you apply an offset to the the data returned from the heading sensor.
As others have mentioned, the shift should not affect your GPS positional data.
As others have mentioned, the shift should not affect your GPS positional data.