Use model.component(<ctag>).mesh(<tag>).create(<ftag>,"Union") to unite meshed entities in 3D. Supported input: entire geometry, unmeshed domains, boundaries adjacent to unmeshed domains, isolated boundaries, isolated edges, and isolated points.
Use DeleteEntities to delete domain elements while keeping the unmeshed domains. If a subset of the faces are selected for the operation, it might not be possible to update any existing domain information. Use
CreateDomains to recreate the domains, if needed,
FreeTri to remesh faces, and then
FreeTet to generate a tetrahedral mesh in the domains.