Is it prescribed to change one's place between the rak'ahs in a single supererogatory regular (ratibah) prayer, or is that specific to moving from a supererogatory prayer to an obligatory one?

It is recommended to separate a fard (obligatory) prayer from a nafilah (supererogatory) prayer by speaking or moving to another spot. The purpose of this is to multiply the places of prostration, so they may bear witness for the worshipper on the Day of Judgment, and this is what the Sunnah brought forth. As for moving between two nafilah prayers, it has not been mentioned in the Sunnah, but there is no harm in doing so if the intention is to multiply the places of prostration. Sheikh Ibn Baz holds the view that performing nafilah prayers two by two (rak'ahs) is preferable, and there is no firm evidence for theability to move between the rak'ahs of a nafilah prayer, but if one does so, there is no harm.