I know AGP can work with *.rbj files created in ArcMap and be reused in AGP but not sure about updating them.
Yes, I agree I am able to do that. It looks like you can't create or update the .rbj file in ArcGIS Pro.
I haven't found a way, either. Creating Reviewer Rules in Pro is similar to creating a batch file (though it applies to a specific map and doesn't seem to have the full capabilities of creating a batch file), but I go back to ArcMap to edit the rbj file.
The issue I found is that I applied attribute rules and upgraded an annotation feature class to ArcGIS Pro version. I tried updating the RBJ in ArcMap, but once you upgrade to attribute rules and Pro version of annotation, it is not able to read in ArcMap. As a result, I am unable to change the RBJ files now.