I'd like to force my callout labels to all line up so that they stack (i.e. their vertical positions change, but they all have the same horizontal start point / easting / vertical grid / x position). Is this possible?
Dear David,
I hope you are doing well,
You can do almost whatever you want with labeling in ArcGIS Pro.
I just uploaded a sample labeling project in my github.
please check the below link and if you need more info please let me know.
https://github.com/AmirSarrafzadeh/GIS/tree/main/ArcGIS%20Pro/Labeling/Fruits
You should be able to see the labels like the attached image.
please check the below url too for more info about composite callout in ArcGIS Pro.
https://pro.arcgis.com/en/pro-app/3.1/help/mapping/text/label-using-a-composite-callout.htm
Hope it helps, Stay Safe