How to restrict dropdown of Dispute reasons under Advanced Collections

Hi,

We are on R12.2.4 and we have the below requirement:-

Under Advanced Collections, when we are creating a Dispute, there is field called "Dispute reason". The drop down values for this field are coming from AR Credit Memo lookup code.

Now, we have a requirement that we do not want all AR Credit Memo lookup codes to be displayed here, we just want only two values to be displayed.

How can we achieve this. I think through form personalization, we can throw a error message if user selects any Reason code other than the two values which we want.