The green rest (secondary downstem voice) had been above the downstem note, but one player is going to play both (this is handbells) and putting the rest below the notehead will make it more obvious.
I’ve learned from the manual vertical movement of a rest is separate from horizontal and that horizontal is handled by Engrave note spacing. But I can’t use that to move the rest independent of the note.
How might I put a tiny gap between the rest and the stem?
That’s odd. If instead of a rest there was a note there, in the Note Spacing tool you’d be able to select its voice column (square handle) then select its individual circular handle and move that. But rests don’t get their own spacing handle, apparently. If this is intentional behaviour I’d be curious what’s the reasoning behind it.
The only pseudo-soution I can give you is to consider if you can hide the bar rest and up-stem the tied C in this instance.
If no better solution shows up there is always the possibility of creating a fake Playing Technique with a quarter note rest glyph (X offset = 10.00) and hiding the real rest, like in this example:
I cannot replicate this. When I change the voice column index of the note, the rest moves along with it. They are glued together in the same voice column.
Edit: Sorry, my bad. I was changing the wrong parameter and you are absolutely right. It is possible to separate them this way.