Can we notify users of a timetable modification by SMS?

Yes. Go to the timetable of the concerned resource, select the course in the grid, then, from the course form, click on the icon located at the bottom left. In the menu that appears, click on Sending of SMS; in the window Editing and sending of SMS, select an SMS template (previously created) from the list on the left, or create a new template.
Once the template is selected, on the right-hand side, verify (if the template has been previously created) or write the content of the SMS.