CUSTOMERS & CREDIT MEMOS:
Open the CREDIT MEMO you wish to unapply, and temporarily change the name of the CUSTOMER:JOB – any name will do. SAVE. This will unapply the credit. Then, change the name on the CREDIT MEMO back to the correct CUSTOMER:JOB. The credit memo is once again fully available and you can apply as you’d like.
thinkQuickBooks 
Perfect …love that little trick!