Beacon is not a financial system like Quickbooks or Xero, so the options for editing invoices are limited (Check out our financial system integrations).
However, there are a few things you can do. In this article we'll walk through how to create an invoice outside the context of a regular case.
1. Create an Event with Event Type "Other". You can use whichever event type makes the most sense to you, but "Other" provides more flexibility.
2. Include context in the Description, comments, and Notes to document why there is a need for this non-standard invoice. Please note that comments may be printed on the sales order. 
3. Be aware, if you are attempting to invoice a distributor or other non-facility entity, they will need to be created as a Facility in order to create the invoice (as a customer).
4. Mark Inventory as used as needed. Change the usage status of the individual items by clicking the pencil icon to designate if items are missing, damaged, etc and make any adjustments to the price. 
5. To add additional non-inventory line items, add "additional cost or adjustments" at the bottom of the screen. These additional line items will appear on the sales order and invoice, but will not appear in sales reporting. In the "Other" event type, you may add cost adjustments with no inventory being present, though this may not be allowed in other event types. 
With these methods you can create a non-standard invoice without creating a case. You may create an invoice without using inventory. For any other questions, please consult this article.