Unless it has changed in version 11, select the script line(s) in the edit script dialog and click the "Disable" button at the bottom centre.
I guess it has changed, I only see Clear and Duplicate there, no Disable.
Tried modifier keys when clicking script lines too with no luck.
I believe disabling script step is available only in the Advanced version. In the Pro version you can use:
If [ 0 ]
Your step/s here
to "comment out" a portion of the script.
Ah, ok, Thx.