Starting in PI AF 2017 R2 you can enable of disable automatic recalculation on analyses in the management tab of PI System Explorer. Please see our User guide for more information on this topic.
To disable backfilling on startup of the analysis service altogether, you would need to edit the Service Configuration for the Analysis Service in the config database in PI AF. That being said, it sounds like the above solution is what you really want.
I tried to disable automatic recalculation for a specific analysis, and after acknowledging that it would affect all analyses made with the same template, I got this message under "Pending Operations".
I guess the Complete flag means it has now been processed, but still half an hour later (and after a Refresh) I will see the backfilling flags in the Analyses tab of the analysis.
Shouldn't these have been removed by now?