[EricH]

TEAM: Four representatives from a registered FRC team that interact with their ROBOT and their ALLIANCE partners to play Breakaway. Positions on the TEAM include:
COACH: A student or adult mentor designated as the team coach and advisor during the MATCH and identified as the person wearing the designated "COACH" pin or button. There is one COACH per TEAM.
DRIVER: A pre-college student team member responsible for operating and controlling the ROBOT. There are two DRIVERS per TEAM.
HUMAN PLAYER: A pre-college student team member responsible for properly returning BALLS to the FIELD. There is one HUMAN PLAYER per TEAM. The HUMAN PLAYER is the only TEAM MEMBER that may handle the TRIDENT.

<G50> TEAM Positions during TELEOPERATED PERIOD - During the TELEOPERATED PERIOD, the DRIVERS, COACH and HUMAN PLAYER may travel anywhere within the ALLIANCE STATION, but they must stay within the ALLIANCE STATION boundaries, and not step outside the designated area. Violation: One PENALTY for each violation. Exceptions will be allowed in cases involving TEAM member safety.
<G51> DRIVERS Operating ROBOTS - During a MATCH, the OPERATOR CONSOLE shall be operated solely by the DRIVERS. Violation: Disablement and RED CARD.

Between matches, anything goes (well, other than an adult driver or human player).

During matches is tougher to call. I'll assume that somehow, you manage to have some way of switching really quickly. Note that if someone is free, they can handle a ball (but the HP has to handle the trident).

Assuming that there is no explicit difference between the HP badges and the DRIVER badges (or other means of identification), you have a tough situation to call if a team decided to trade positions other than coach during a match.

WITHOUT Q&A clarification, I'd have to say driver-driver trades only.

WITH Q&A clarification, who knows?

I'd say to ask Q&A.

Gary, got anything that I don't (e.g., ref-only material)? I can't find anything in the rules to support that you can't switch during the match. The only Q&A I can find on the subject is http://forums.usfirst.org/showthread.php?t=13811, which simply says that you can't give up one position to get an extra in another position.