How does the Import in the Customize the Ribbon tool work? When you Import a .proExportedUI file, it asks if you want to "Replace all existing Ribbon and Quick Access Toolbar customizations?" So I guess that means that you can't send a co-worker just a new Tab/Group. You would be exporting the whole ribbon configuration. But what about further customizations? I created a New Tab and a New Group and put some tools in it. Then I exported it. I Removed it, because I was teaching an inhouse class and didn't want to confuse my students with my strange Tab. Now I Imported it back, but when I tried to add additional tools to my Group, after I clicked OK, my new Tab disappears. Do new customizations cancel out whatever was imported?
I'm using ArcGIS Pro 2.5.2.