Hi dex
Ideally you can have any value in it and is defined in the below SPRO path .
In Partner schema You can do following :
1. Create the partner schema. Enter a 4-character ID, a description, and a long text for the partner schema.
2. Assign partner functions to the partner schema. You can specify the following:
- The levels (that is, header or item level) at which the partner function is used in the schema
- How often the partner function is used
- Whether the partner function can be displayed or changed on the user interface
- Whether the corresponding address can be displayed or changed on the user interface
- Whether the partner function should appear on the user interface at all
- A name for the partner schema (this name will appear in the hit list for the search help)
Now assign transaction types to the partner schema in the Define Transaction Types. This establishes a link between the partner schema and the purchasing document.
if you want to put some logic try doing so in BADI BBP_DOC_CHANGE_BADI and in that the method :
BBP_CTR_CHANGE
let me know if this helps
Regards
Vinita