Yes. You can edit the content of the invoice from the main Invoice Grid under the Transactions & Invoices Module and click on the row with the invoice to edit. Click on View/Edit, then select Invoice to open the invoice. Or from an constituent's record under their Invoices Tab. Click on the row and click View/Edit to go to the invoice.
From the invoice page you can edit as necessary, including adding new line items or outstanding balances to the invoice. You can also edit an individual line item by clicking on the Edit Icon. A new window will open to edit the information for that line item. Click Update to close the pop up window, then click Save or Save and Print to complete the edit.