Yes. A path attachment is a VertexAttachment. You can grab the vertices and change them as you wish. For a path, the vertices are triplets of x,y pairs for each path point: c1x, c1y, vx, vy, c2x, c2y. That is: the first Bezier control handle, the vertex, and the second control handle. There are always 2 control handles, even for the first and last point of a non-closed path.
Note that a path is an attachment and attachments are stateless and shared across all skeleton instances, shown here:
Runtime Architecture - Spine Runtimes Guide: Class diagram
If you modify the path, it will be modified for all skeleton instances. If you only have one skeleton instance, you may not care. Otherwise, you would want to duplicate the path attachment for each skeleton instance.
You will likely find it easier to weight your path to a bone, then at runtime position the bone to control the path. Bones are part of each skeleton instance, not shared across instances, so there is no need to modify the path attachment. You can see a live demo in your browse of this technique (drag the red handles):
Spine: Demos: Path constraints
The code (filthy JavaScript) is available, but it's not terribly interesting since simply moving the bones is what deforms the path. Most of the code is just loading, setup, input, and rendering. More interesting is the vine demo project which you can open in Spine to see how it works. Select the weights tools to see how the path is weighted:
Loading Image
Move the vine-controlX bones to see how the path deforms. IK is used so each control bone points at the next control bone, which is one way to get the path to bend reasonably when moving the bones.
The stretchyman demo (immediately below the vine demo) also uses paths weighted to bones.
