About the Import and Update of Multibodied CAD Models
When you import a multibodied CAD model, a TIM assembly is created with each body represented as a separate TIM part. However, all these CAD documents are considered as a single packaged content. This content is primary and the multibodied CAD model is a single CAD document. This CAD document is automatically associated with the WTPart of the source CAD document. That is, only the top-level assembly is linked to the WTPart. The components in this CAD document are associated by an indirect type of derived link.
Additionally, you can only update the entire geometry of the TIM assembly and its individual component TIMs. Therefore, the multi-bodied TIM assemblies are inseparable for actions such as Save As and Revise.