I haven’t found anything that prohibits this, but is it legal to launch your preload at the beginning of the match at the other alliance?
to some extent.
here are the relevant rules:
<SG4> Stay out of the opponent’s Home Zone during Autonomous. During the Autonomous Period, Robots may not contact the foam tiles, Mobile Goals, Robots, or Platform which is/are in the opposing Alliance Home Zone.
<SG10> Use Scoring Objects to play the game. Scoring Objects may not be used to accomplish actions that would be otherwise illegal if they were attempted by Robot mechanisms (e.g., Interfering with an opponent’s Autonomous routine per <SG4>.)
So throwing a ring into your opponents home zone would be illegal. But launching a ring into the neutral zone is entirely legal, and might be a viable strategy if you can reliably not overshoot into your opponent’s home zone, perhaps in the space between their home zone and the tall neutral goal.
Some robots are launching rings onto goals and that is the way they will score.