Can I edit files come from .vfl in VEX Builder?
I downloaded some .vfl, .vex and .ds files from the web,
and the many Houdini's default SHOPs have the .vfl and .vex file,
I want to make a study at that in VEX Builder.
I have used vcc command to create the .vex and .ds file,
moved the .ds file the shop/surface,
modified shopsurface file by adding
“v_NAME shop/surface/NAME.ds -label ?gVEX_NAME?h,
then can use it in SHOP well.
But can't edit the SHOP.
Right-click the SHOP icon, can't select ”Edit VEX network".
If yes, how to do?
Thank you.

Unless the shader was build in the VEX Builder, there is no way of taking hand written shader code and having the VEX Builder build a network from that.

You can turn that shader in to a VOP operator so that you can use it as is in the VEX Builder though. Just add your custom shader in the SHOP network, then RightMouseButton on the icon and select:
Create New Vop Type…
and follow the insructions. You should then be able to Tab-select in the VEX Builder that new node. This is how you would mix two different shaders together.

Thank you.