Ok. So I've done the unthinkable.

I've made most of my changes on the default template on a test shopping cart, which is ready for showtime.
I'm on godaddy. How can I remedy this (i.e. create override) before taking the shopping cart live? Apologies if this is clearly posted somewhere. I see all the help to do the override, but I cannot make the link to the obvious, how to override after you've done your changes? Is that even possible?