Expense Report Paid Status?

<p>Hello-</p><p>Is there a way to indicate that after an expense report has been paid (a person has been reimbursed) that we can change an expense report to "archived" or add a check box "paid"? However, an added custom field can't be edited once approved...</p><p>Our accounting wants an easy way to see which expense reports have been processed.</p><p>Thanks for the help,</p><p>Marc</p>