Ability to Customize the invoice block

The invoice block is a nice feature but it does not have any ability to edit and this makes it useless for any business that does not sell exactly as the table is setup. The ability to add, remove or change the merge fields would greatly expand it's effectiveness and use

As an example a company has online only products that are never paid in full. In this instance the taxable column might not be needed but a total price column would be as the person would be paying only a down payment and the total price needs to be present