Studio is an Intersystems provided tool to edit routines/classes/xml/ etc. used in Caché systems, it isn't a general purpose editor.
If you have a valid Caché system, you could pull up the GT.M routine in a linux editor like pico/nano, copy the entire routine into the clipboard, then paste into a new .MAC routine in Studio for editing, then when done, copy/paste back into nano and save. A lot of effort that doesn't add any value.
I highly recommend Serenji if you are going to edit/manage M systems on multiple vendor platforms, it is very good.
Mark
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I would also recommend you post the question on the Hardhats google group, that is where the majority of Vista related questions/answers are.
https://groups.google.com/forum/#!forum/hardhats