A slight modification.
Sub AddCodeToThisWorkbook()
Dim i&, s$, s1$, pthTmp$
s1 = " Application.Run" & Chr(34) & "'" & pth & "'!ShowForm" & Chr(34)
With ThisWorkbook.VBProject.VBComponents("Module1").CodeModule
For i = 1 To .CountOfLines
s = .Lines(i, 1)
If s Like "*Application.Run*ShowForm""" Then
pthTmp = Split(s, "'")(1)
If pthTmp = "" Then
.ReplaceLine i, s1
Else
If MsgBox("Whether to replace the path?" & Chr(10) & pthTmp & Chr(10) & "to" & Chr(10) & pth, vbYesNo) = vbYes Then
.ReplaceLine i, s1
End If
End If
Exit For
End If
Next i
End With
ShowForm
End Sub