It is here! Big excitement!! You can now edit your new Blogger Beta template. I have just found out and am researching it. At first glance it seems things are a little different. Just scanning the documentation, the new template language is completely different from the original one. There is much talk about widgets and sections...oh my.
So, above all, save your template before doing anything. Another way to experiment without damaging your orginal template beyond repair is to open an experimental blog and paste your template in. Go from there.
Here are a few links to get you started: