It's known that for the first showing of the Excelsior
-class model in "Encounter at Farpoint" that they changed the registry to NCC-2541 from NCC-2000. Subsequent footage of the model was either stock shots or a new shot using the model with the Hood decals on. (The new shot was first seen in the episode "The Child".) It appeared that they changed the registry on the upper saucer and on the nacelles. They may have changed the registry on the lower saucer as well.
For its appearance in the sixth movie, the Hood decals were removed, and new Excelsior decals were applied.