How do you unapply a commitment?

 My company takes a lot of deposits prior to doing work.  We receive the customer payment, which is applied against a deposit invoice (commitment).  That commitment is then applied to an invoice.  Due to user error, we later find that the commitment was applied against the wrong invoice for right customer, or wrong invoice for wrong customer.
I've been trying to find a way to unapply that commitment.  What I've seen so far is to do the following:  Issue a credit memo against the invoice in the amount of the commitment.  This frees up the commitment amount, which can later be applied against a different invoice, assuming on same account.