As a PM, I can notify by email changes on assignations
The Project Manager (PM), also PMO, PMA, PfM and PgM, can email changes on assignments at CONTROL > Control Resources > Team Members/Assignments:

Click button [Notify] to send an email to the TM containing the information on screen.
Frequently Asked Questions
Who can send assignment change notifications by email?
Project Managers (PM), PMO, PMA, PfM, and PgM roles can send email notifications about assignment changes.
How do I notify a team member about assignment changes?
Go to CONTROL > Control Resources > Team Members/Assignments and click the [Notify] button to send an email with the on-screen assignment information.