Currently MPMLink does not allow to specify what kind of documentation is propagated to downstream branches/parts based on document subtype. In fact there are kinds of documentation which are not needed for manufacturing purposes, so it would be beneficial to really only propagate those document links which are related to the equivalent downstream branch/part.
The current properties only allow to define the link type, meaning that whether all or none describing (Described_by link) or referencing (reference link) documents will be linked to downstream branch/part. Being able to differentiate between specific document subtypes it would be necessary to subtype the links (Desribed_by, reference etc.) which is not an option.
Furthermore it should be considered, that the property is also reflected in other MPMLink functionalities, such as reconciliation assistant/Update equivalent link with propagating upstream changes to downstream or automatic BOM transformation (GDS).