Yes you can change or edit just one single instance of a recurring event.

Double-click on the specific event you want to change.

A dialog box should appear.

This event: This changes only the instance you double-clicked. The rest of the series remains unchanged.

All events: This changes the entire series from the beginning.

Make your changes time, location, title, etc. and save.

Create a recurring event

Hello George, That's exactly the approach I used, but the recurring appointment is not being changed. I have an Termin; Lunch every Day and when it will be chanced it will not going on.

Is your calendar a local calendar stored directly in Thunderbird or is it a network/remote calendar (like Google Calendar etc?