The more involved that you get with your blog, the greater the chance is that you or the blogging service that you're using will mess it up radically. So here is a bit of advice to myself as much as anyone:
Backup / Restore TemplateBefore editing your template, you may want to save a copy of it. Download Full Template....(Blogger: Settings: Template: Edit HTML)
You do want to backup your template before you radically change it, don't you?