To use a different EPG, yes, the tuner will need to be removed from Plex and re-added. However, your recording schedule will not be removed, but there is a chance that they won’t work and you will have to remove and reschedule them.
Indeed some recordings will continue while others will be ignored. The issue will be the title of what one EPG calls it vs the other. For example, my series link of The Office needed to be deleted and reset with the new IceTv DVR because IceTV calls it The Office ( US ) while the Gracenote one called it just The Office.
So yes, look at what the coming recordings are and match against the expected recordings.