I have a S4 MK3. I want to adjust the size/number of beats of a single sample in a Remix Deck. I know this is possible via a Kontrol F1. I haven't found a way to do this via the Traktor Pro 4 UI or the S4 MK3.
It is not accessible from GUI unfortunately but you could map some keys on your keyboard.
TP 4.1.1 has problems with this exact thing at the moment. You can change size, but it reverts to the original size as soon as you change the sample cell in the same slot (column).
Pardon my ignorance, I've tried to map the controls but to my keyboard so I don't interfere with my S4. However, it appears that when adding a control to, say, Slot Size x2, I then have to map it to a specific Deck and Slot… this might be a misunderstanding though. But I have not gotten this mapping to work yet. Will keep trying in case I figure it out and report back for posterity.