Change Aggregation Level for WPUUMS

Hello! We're very new to POSDM and we can't seem to figure out how to change the aggregation level from article to tax code. The client wants the WPUUMS IDOC to send from an article/tax aggregation level.

Ex:

1st IDoc

Article: COK01

Sales: 1120

Tax Code: O1

2nd IDOC

Article: COK01

Sales: 1100

Tax Code: O2.

How can we do this in POSDM?

Thanks in Advance!!