Repeating IDOC segments

Hi,

Can anyone explain why and which is a better option among

Repeating an IDOC segment to populate some additional data or extending a segment to populate the data.

I would like to populate supplier code in E2DRM1 segment- Partner_ID field of IDOC type QALITY02. The SAP's standard populates ADRNR number from the KNA1 table (in transaction code QC20). But in transaction QC22, I dont see this segment. How to populate this segment?

I appreciate your response.

Shiva