It's not really very difficult to shift rows or columns with zl rot, but it does take a few objects and a bit of work. I tried making the simplest version I could in the patch below, but it's still kind of busy for the results. A direct message to [matrixctrl] like "shiftrow " would be great, where the shift amount works just like [zl rot] and excess values wrap.
It might also be nice to have a fill command:
though this is pretty easy with [uzi] and [%].
If there's a simpler way to do the shifting that I'm missing, then by all means...