The pull to refresh widget allows you to sync the data to your device based on a pull.
It doesn't allow you to call a microflow afterwards. I can't see why you would need to be honest.
If you trigger a sync then you could use a before commit microflow to do some changes to the data. This before commit will get triggered when new or changed data is synced from the device.
Your other option is extend the widget to support a Microflow or nanoflow call.