Fabrication Parts in Revit don’t always allow editing of their Material or Specification properties. Look at the below side by side images. Revit’s properties can be seen grayed out on the left but those on the right are not.
Revit can obscure the reason for this because you have no access to edit your Fabrication Database within the Revit environment. The answer however is quite simple.
Fabrication Parts with the “BoughtOut” property set do not allow editing of Material or Specification. After all, a bought item is typically static and can’t be easily changed. Non-BoughtOut items do allow editing of the Material and Specification properties.
The following is another side by side image of Fabrication Part properties. The properties on the left have the BoughtOut property set. The properties on the right do not have the BoughtOut flag set. While not accessible from Revit, any of the other Autodesk Fabrication products can display and edit the BoughtOut property.