Yes, renaming categories in Revit is impossible, because as Aaron stated they are hard-coded. They also are the family categories names and once again the Revit software does not permit renaming the family categories, or how else wood it know in both Visibility Graphics and Object Style what the model and annotation category are named.
Mel Persin, AIA
AEC Technology Consultant
Technology to Visualize and Realize Solutions
MasterGraphics, Inc.