In Core, when you set up client profiles, you can also add contacts for each client. One of the client contacts can be set as the main or primary contact.
If needed, you can assign a different contact to a project from the client contact. If you select a project contact and then select the option 'Send Invoice to Contact', then Core sends the project invoices and statements to this contact instead of the default client contact. In addition, the address of this contact overrides the client address and prints on invoices and statements.