2020-04-17 : If you choose the first mode and the creature gains a counter in response, you can’t remove counters from it instead; the spell just doesn’t resolve. Similarly, if you choose the second mode and the creature loses its counters in response, you can’t destroy it instead.

2020-04-17 : If you choose the second mode for Heartless Act, you choose which counters to remove from the creature, no matter who controls the creature. You may choose counters of different kinds.