Hi,
Navisworks is a kind of product that manages the model. It has not the ability to 'design'. So it cannot edit the model elements such as adding new objects, deleting them or spliting. neither does API.
about adding new objects, an approximate way is to append a new model (say a model with the specific element only), but it cannot be merged to the model structure of the base model.
about deleting, you can only make the visibility of the object by Hidden methods.
as to spliting, you have to turn to the design software of the orignal CAD file.
