What is the purpose of selecting an Entity on the Datamart Settings page?
The Datamart entity is only for setup purposes and is used as a 'default' bucket for any non-financial investments. Investments linked to other entities will still show up in the Datamart tables. The Datamart Entity is also used for retrieving the active, Monthly Fiscal Periods for the Datamart Fiscal Period table.
The Datamart Entity field can only be set once and cannot be modified. The Datamart can not be linked to multiple entities, however resource and project information will still preserve their own financial properties for Department and Location Entity associations.