yes, perfectly possible, you will need to detach from original template, then save as a new template, and name all your template regions etc the same as the old one, or it won't find and update the same places on the pages. Must also be named the same as the old one, so re-name the old one.
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Sometimes, when my code just won't behave, I take it outside and make it listen to britney spears music, and when it comes back it's really well behaved. I wonder if it's suffering from post tramatic stress syndrome now..