@CraigWeb We just tried to make this change and I noticed a couple of things.
There is no option for setting intervalLoggingType once you've set loggingType to "Interval and when point value changes" via the GUI.
We ended up just changing the JSON and pushing that out, which it seems to have taken the changes.
Also interesting, when hitting the API endpoint for data point details...if the point is configured as ON_CHANGE_INTERVAL it does not return a key for "intervalLoggingType" nor is any value for any keys set to "AVERAGE" but I certainly do see those for points configured as "INTERVAL"
I honestly always assumed the way ON_CHANGE_INTERVAL worked was it logs on changes and the current value once per minute, I had no idea this would be averaging over that minute and then recording the average.
Anyway...I'll let you know the results, just wanted to give that info.