How to change (user dialog preferred) the assignment between personnel number and business partner?
Let's say move "1" from 9980000020 to 9980000010.
Could be a user error or switching from "no HR integration" to "HR integrated".
The system seems having memorized somewhere 1-to-9980000020 linkage.
Playing around with TCodes BP, PA30 and SU01 does not help.