BAPI_USER_ACTGROUPS_ASSIGN deleting roles

Hello,

we are trying to create a process where we can change the "valid to" date on a role for about 400 users. this process will be done once a year. I have found a bapi "BAPI_USER_ACTGROUPS_ASSIGN" that I can call in a program. the process will be to use a csv file containing the data and read it in the program and call this bapi to update the date.

I am testing the bapi in SE37 with a user that has multiple roles. I add the role and the new date to the ACTIVITYGROUPS table and when I run the func module, the role gets updated with the new date but all of the roles there were assigned to the user are now gone.

I have search SDN and I could find anything that references this issue.

has anyone else had this problem and were you able to correct it?

Am I running the func module incorrectly which is cuasing the roles to get deleted?

thanks in advance for the help