Hey there, I also wanted to be able to adjust the Panner X/Y speed from a material instance, so I created a custom Panner node.
Basically what I did was create a new MaterialFunction that is a copy of the Panner node, but with and additional input for the X/Y speed, and I now use it anywhere I would have used the Panner node.
It is a fairly simple setup as you can see here:
But let me know if you can’t get it to work, I can send you the uasset file if necessary.
Hope that helps!