@Dogtags, I started with the edit order contrib, and eventually coded out of it due to the issues sanji is describing. I dumped the actual product editing for these reasons and kept all the other stuff. I know that someone has kept this mod alive, but as far as I know nothing has been done to address these tax and attribute issues.

The next version of SO has the ability to perform returns and exchanges, which should (slightly) address this issue. You won't be able to edit an existing product, but you can replace it with the same product and alter the qty, tax, attributes, etc.