Hi,
There are many active standard implementation for BADI Partner_update which are as follows :
BUPA_OUTBOUND_CREATE
CRM_BUAG_BW_UPD
CRM_BUPA_ES_UPD
CRM_BUPA_SEG_UPDATE
CRM_BUT_TDTRANS_UPD
CRM_CHM_BUPA_UPD
Please go through the code written in method CHANGE_BEFOR_UPDATE of these BADI.
BADI PARTNER_ACE_UPDATE would solve your issue.
Thanks & Regards,
Akshay Ruia