When I view two files (bimserver, local, aat) in Attribute Manager, I would like to have a 'Compare' button much like those that show changes in text files, highlighting in each list new attributes say in red and modified attributes say in yellow.
Though it might be a bit dangerous, if you select all and apply by index, then hit apply, the dialogue that comes up tells you everything that is new and what has been modified. I think AC22 may have answered your request though as I remember seeing somewhere that they removed this follow up dialogue in favour of something more streamline.