I've heard you can schedule big sales all the time and then regularly cancel them unless something goes wrong. Apparently there is no rule against insider canceling.
https://corpgov.law.harvard.edu/2013/02/05/rule-10b5-1-plans...
I am no lawyer, so I don't know if this is really allowed. My gut instinct is (a) no, it is not allowed and (b) there will always be some more subtle version of the tactic that is allowed.