Mapping a group to an offline segment in Luminate is not a two-way sync like with some other data that synchronizes via a data sync operation or the service bus. When you map a group to an offline segment, it is basically just a query group that queries your offline database whenever the group rebuilds to obtain up-to-date information. While you can use this group in Luminate just like any other group, any changes will have to be made in your CRM and allowed to sync down to Luminate the next time the group rebuilds.