I got some new hue bulbs over the weekend and replaced a few older ones with them and came across an odd observation when trying to update some of my button controller rules that controlled those bulbs. There were a few buttons that were easier to delete than to edit but upon trying to delete say button 5 doubletapped, I noticed it does not allow you to delete just the doubletapped action of button 5, you have to delete all of button 5's actions (pushed, held, doubletapped, etc). Depending on your situation this could be troublesome. Hadn't seen this mentioned before and maybe I am missing something, I haven't played around with button controller a whole lot since tables and what not were added.
You can delete all of a button rule's actions by hitting the delete (trash can) icon at the top of the action table, i.e., in the header row. You do have to go into the button rule to do this (I think this may have been possible from the main page before?) but is effectively the same outcome. You could probably also delete the grandchild app itself from its App Status page, though I don't like ripping child/granchild apps out from under the parent if I don't have to (not sure if inability to get into the button rule itself is what you mean with "troublesome," but this would be the workaround for that).
Sounds like you've noticed you can delete all actions for a particular button number by using the "-" icon at the bottom of the table, so this is an alternative if starting over is easier with just a particular number plus action/event combination.
Oof, totally forgot to mention the reason I got stuck not being able to delete the specific button from within the button was because of another bug that is supposed to be fixed either in the most recent update or the next one. So it most likely won't be something that comes up often (if at all anymore) but it would be nice to have the option from the main table view of all configured buttons.