Here's an updated keymap for a Drum Overview Grouped...it renders a muted item to the folder track, which is automatically grouped with the child track items.
So, whatever you do to the overview with splitting/editing etc is also done to the child tracks...pretty cool!
Here's the map:
https://stash.reaper.fm/oldsb/174298/...ew-Grouped.rar
Unrar the file, then press the (?) key for the actions window, press import, choose Drum Overview Grouped.ReaperKeyMap...it's mapped to Ctrl-Alt-F10 as is, change that to whatever you want.
Here's the actual macro: