Is there a rule against connecting preload rings together (using zip ties, rubber bands, other vex-legal hardware) such that the hardware remains attached to the robot when the rings are let go?
As long as rings can be removed without having to turn on your robot/break something, yes this is legal.
important things to consider:
i. No Preloads may be contacting more than one (1) Robot.
ii. All Preloads must be fully within the field perimeter.
iii. All Preloads must not be in any positions that would be considered Scored if the Robot were not present. See Figure 21 for examples of legal Preloads.
<G17> Let go of Scoring Objects after the Match. Robots must be designed to permit easy removal of Scoring Objects from any mechanism without requiring the Robot to have power after a Match.
if you don’t violate either of these two things, then you’re good.
unless I’m misunderstanding and you intend to have a part of your robot detach and hold the rings together, in which case you would be in violation of <g5>
That indeed was the original idea, but yes, you’re right, we realized it’d be against G5.