Is there a way to configure the e-mail notification in such a way that when a project manager changes a supplier, the original supplier receives the e-mail stating that the job is no longer assigned to that person?
Yes. Solution is to turn on notification "Notify unassignment of worker at supplier"
This notification is send to the worker who was previously assigned. The notification title is "Job revoked from supplier". The project manager does not receive a copy of this mail.