So, rule R1 forbids a team from making any major changes to their robot during a competition, i.e. completely removing a lift. Would simply moving a motor from one mechanism to another count as a major change.
Moving motors between mechanisms during a competition
Correction - R1 forbids creating a second robot by “swapping out an entire subsystem of either item 1 or 2”. Swapping out subsystem 3 (“additional mechanisms (and associated motors) that allow manipulation of game objects or navigation of field obstacles”) is allowed.
This is reiterated in the official Q&A here: https://www.robotevents.com/VRC/2018-2019/QA/27
Swapping out subsystem 3 motors, therefore, is fine.