Removing the Reference Link in Interface Lines Table to create On Account Credit Memo

Hi,

I created an Order in OM with 3 lines. This  order interfaced into AR with 1 transaction and 3 lines. Later i created an RMA for this order. The RMA has 2 lines. I am running a SQL Script to remove the reference_line_id from the Interface Lines table so that on account Credit memo can be created. The SQL Script ran and On Account Credit Memo got created but 2 separate Credit Memos instead of 1 Credit Memo. If i want to prevent this from happening what conditions should i use in my SQL Script so that the RMA does not get split?