When changing only one of a repeating event, it is possible, the option where to choose which one to change is at the bottom of the page though and you have to scroll to find it. It would be a lot easier if it were at the top!
Steps to reproduce:
# Create repeating event
# choose one of the dates and click on change
# go to bottom
You have to scroll and option "change all" is default.
I can see at the top on first sight which one I am going to change, and can change it here (maybe option "only this event" should be default?).