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Once set as 'draft', any changes made will not be sent out to your staff until you have marked the roster as 'Published', by clicking 'Mark as published' (see below).
Bulk changes
Changes to rosters, marking them as published or back to draft can be done via the events list - just select the events you'd like to change, and select 'Roster settings' at the bottom of the list in the 'choose an action' dropdown;
Hiding draft rosters
If you wish, you can set the configuration to hide rosters while they're in 'Draft', so they're only shown when the roster if finalised.
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