Official Q&A: VRC 2018-2019: Turning Point
27: Clarification of <R1> and <R2>
Rule <R1> allows teams to replace subsystem 3 during a competition, such as a flywheel, cap lifter, scissor lift etc, whilst rules <R1> and <R2> limit teams to only having one robot at a competition:
Would a team be allowed to have spare subsystem 3s for their entire robot if they are identical to the subsystem originally on the robot? Would having replacement subsystem 3s for all the parts of the robot class as being a second robot effectively for spares, breaking rule <R2>
This is because we intend on building a modular robot where each subsystem 3 can be swapped out with ease, whilst keeping the same subsystem 1 and 2
Yes, this is legal. As you noted, <R1> only prohibits teams from swapping Subsystems 1 and 2. Remember that if you have multiple configurations with different Subsystem 3 mechanisms, your Robot must be inspected in all possible configurations per <R2b>.