Updating an existing pipeline schedule variable #3063

The documentation only covers updating a schedule variable that was created. The only returned from create is

is a ProjectPipelineScheduleVariable whereas schedule.attributes["variables"] returns a list containing dicts (see screenshot).

schedule.variables.create and schedule.variables.delete can be used directly but I'm unable to use schedule.variables.update directly.

What is the correct way? Also, will update fail if the variable does not exist or is it simply created?