This actually simple solution I stumbled upon while working together with Esri Support to define an enhancement for ArcGIS Pro. And it can also apply to other ribbons.
Default it is not possible to apply transparency on the level of a Discipline or when selecting the added Revit file in the TOC.
When you added a feature layer or made a group layer it is possible to apply transparency. When added a Revit/IFC model to ArcGIS Pro it is possible to apply transparency to Categories in a Discipline. You can select manually one or more Categories and apply a transparency to them. It is inconvenient when working a lot with Revit models in ArcGIS Pro and go over these steps manually every time.
1. Select the Revit file in the TOC and right click on the tab ‘Manage’ > ‘Customize the Ribbon’
2. Choose commands from: ‘List of Tabs’:
3. After customizing the Tab Building, when selecting each level of the added Revit file you can apply a transparency to that level. When you select a category also the ribbon Feature Layer will appear but that is default behavior.