Hi Bob,
Not at present unfortunately. AtoM's multi-institution functionality was added after its initial development, and was originally intended to support multi-institutional access rather than management - the use case was primarily a single administrator supporting a portal site or union catalogue and managing contributions from other contributors with their own access systems. The way that people want to use AtoM has changed significantly since then, but the development required has not fully kept apace - so currently there's no entity link between an institution and an accession, or the ability to maintain separate per-institution accessions modules.
It would be possible to introduce in the future, but it would require significant development to change the underlying data model and user interface.