Can a PVD affect my performance as a competitive marksman?

When the posterior vitreous detaches in a PVD it causes floaters, which can potentially interfere with vision. However, a systematic shift in your ability to aim at a mark accurately should not be affected by the PVD. Perhaps you can consult your ophthalmologist and retina specialist and they could look for eccentric fixation (when an area in the back of the eye, other than the fovea, is used for visual fixation), which theoretically could cause a systematic shift such as you are describing.