Allow invoice fields to be changed on edit even when a partial payment is applied to the invoice.

All fields on an invoice should be editable except those that affect price.

The following fields cannot be changed on edit when a partial payment is applied:

• Invoice line item quantity
• Invoice line item amount
• Invoice line item tax
• Invoice currency
• Adding a new line item
• Removing an existing line item

It's sometimes necessary to change the bill or due date of an invoice without changing anything else. For example, a customer wants more time to pay the remaining balance on an invoice and you don't want to use the delay suspension option because you want other services to be suspended or don't want them to receive anymore late notices.

It may make sense, when editing an invoice, to ajax-save the bill/due date automatically (and indicate that it was saved next to the field).

This is somewhat related to CORE-8 which allows the editing of public/private notes when partial payments are applied.

Ultimately it may make sense to combine these tasks and allow anything to be updated that does not affect the price of the invoice. More discussion may be necessary.

See original request at http://www.blesta.com/forums/index.php?/topic/6301-change-invoice-has-a-partial-payment/