Please remember to quote the applicable rule from the Game Manual in your question. Rule G6 states the following:
<G6>Drive your own Robot. Each Team shall include up to three (3) Drive Team Members. No Drive Team Member may fulfill this role for more than one Team in a given competition season.
When a Team qualifies for a Championship event (e.g., States, Nationals, Worlds, etc.) the Students on the Team attending the Championship event are expected to be the Students on the Team that was awarded the spot. Students can be added as support to the Team but should not be added as Drive-Team Members or programmers for the Team.
An exception is allowed if one (1) Student on the drive team or a programmer on the Team cannot attend the event. The Team can make a single substitution of a Drive Team Member or programmer for the Championship event with another Student, even if that Student has competed on a different Team. This Student will now be on this new Team and may not substitute back to the original Team.
Violations of this rule will be reviewed by the REC Foundation and may result in one or both Teams being disqualified for the event or the remainder of the season with all trophies and awards won that season being nullified.
As with all rules, this rule should be read with <G3> ("use common sense") in mind. The intent of <G6> is to prevent the same Student driver to operate / compete with multiple Robots across multiple Teams simultaneously. If a Student permanently changes Teams for reasons including (but not limited to) illness, changing schools, or conflicts within a Team, then that Student may drive the new Team's Robot, regardless of whether or not the Student drove the previous Team's Robot.