Hi Saby

It sounds like the roles are being assigned through an audience if changing the employee type has resulted in the role being assigned.

Are you able to find an audience that has a rule in it that selects these users and select the Assign Roles tab?

Next select the role you want to unassign and select all of the  existing users and click 'Remove' from the role.

It doesn't look like there is an automatic way of assigning the role through the audience rule as there is a button that needs to be pressed to action this.

Regards

Craig