Converting a non-posted Misc Invoice to a Credit Memo

within 9.05.701, does anyone know of a way to change a MIS Invoice to a MIS Credit Memo.  I'm in the AR Invoice Entry process, and I accidentally created a MIS Invoice, started to fill it out, saved it, and got an invoice number.  It's not Posted yet.  However, I should have selected this to be a credit memo at the beginning.  I would like to avoid deleting it and making a new credit memo because i want to keep the invoice#.  

I suspect this request can't be done for a control purpose.