Since a driven dimension cannot be dragged, you need another piece of geometry to drag.
This is the reference I built. It is as you defined but if neither parameters are met, it revert to "1".
Dim d0 is the length of a line in the sketch. It can be dragged as desired.
d1 set the length of the extrusion. This references the "state" of d0 to analyze the intended length.
If in fact you only want the two length, then all you need is a division at <=10
If you have a lot of steps, you might even use the graph to manage acceptable length. Much easier and more logical in my view. X would be applied to d0 and Y... a step graph, would be applied to d1. I posted more info on using graphs here: Using Datum Graphs in Relations
This is a quick video of what the above illustration does when dragged:
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Why is dragging so important? Most people deal with this in family tables if I'm not mistaken.
