InDesign does some messy stuff with creating css styles and the html tags that point to them. That's why I don't use its automatic tagging. You can bypass all this and create your own CSS sheet that you can give your client. The stylesheet can contain styling for all your paragraph styles (classes) and object styles (divs). On Epub export, there is an option to add your own stylesheet. Then create an export tag for blue box_head. The fly-out menu on the Paragraph Styles pallet has an option to edit all export tags at once. I think when you save the template for your client, all the epub export setting will be saved with it. You can just give your client the css sheet and the InDesign template.
Still though, I have not been able to make an epub from InDesign that requires no editing after it is in epub form. I always have to go in and tweak some things.