Renaming multiple wires using wildcard

That's not what net expression means. Net expressions are where you set up inherited connections, and they allow the name name to be defined by an expression (in a specific syntax, not a regular expression).

Whilst you can find a net name using a regular expression, you can't replace the net name using components of that regular expression. You can however do this pretty easily in SKILL (I'm assuming it's wire labels you're trying to modify; this code below only handles wire names and doesn't try to fix pins which renaming - that could potentially be done too, but is a little more work). Here's the code:

procedure(CCFrenameLabels(pattern replacement @optional (cv geGetEditCellView()))
  let((netName newName patObj)
    patObj=pcreCompile(pattern)
    foreach(shape cv~>shapes
      when(shape~>objType=="label" && shape~>layerName=="wire"
        netName=shape~>theLabel
        when(pcreExecute(patObj netName)
          newName=pcreSubstitute(patObj replacement)
          shape~>theLabel=newName
        )
      )
    )
    t
  )
)

Here's how you might use it (in the CIW):

CCFrenameLabels("(.*)_0(.*)" "\\1_1\\2")

The parentheses capture that part of the match, and then the \\1 and \\2 reference the matching parts in the substitution value.

Regards,

Andrew