Hi Grampa,
I do not think the plan can be halted typically.
Can a Rule 10b5‐1 plan be modified? While amendments to Rule 10b5‐1 plans are permitted as long as the modifier does not possess material non‐ public information at the time of the modification and meets all of the elements required at the inception of the plan, modifications should be avoided because they create the perception that the person is manipulating the plan to benefit from material non‐public information, jeopardizing the good faith element and the availability of the affirmative defense. As a result, Rule 10b5‐1 plans should be modified rarely and should be designed to prevent the need for amendment.