Ex is not really the best command to perform such complex tasks (I assume that cutting each note of a retrigging note group is complex).
If I was you, I would expand the pattern, or the section of the pattern where you want to apply such kind of effects, or in general use an higher LPB (Lines Per Beat) value in the song, to achieve more control over the single notes.
An LPB value of 12 would let you easily control note groups of 1/2, 1/3, 1/4, 1/6 each.