If I edit a recurring event, do all occurrences change together?

No. You can choose the scope of the change when editing.

• This event only — Changes just the selected occurrence (others are unaffected)
• This and following — Applies to the selected date and later occurrences
• All — Applies to all occurrences, including past and future

Deletion supports the same three scopes. Please be careful with the scope selection when editing so you don't unintentionally rewrite past events.