Hello,
Removal on the mean of the motion parameters will have no effect on any beta of interest, as it will only affect the polort 0 betas (and stats), which almost no one ever looks at. Is that what you are concerned about?
Adding a constant term to any regressor, even per run, will have no effect any beta but the polort 0 ones. Well, more accurately, it would have no theoretical effect, though one might see *tiny* computational truncation differences.
- rick