Duplicating termplates

I have a termplate which I have built with a lot of customisation. I want to maintain this template for future use but create another one which is very similar but not the same. Essentially what I want to do is take the current template do a "File>Save As" and create an identical but new one that I can then tweak a little bit. I can then flip back and forth between the two templates as needed. For the life of me I can't figure out how to do this. All I can seem to do is to build a brand new template or modify the existing one. Can anyone help please?