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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).
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.
Your staff will still be shown events they're rostered to as part of their upcoming events, but the event will be flagged as 'draft' so they know the roster isn't yet finalised.
Do this this, goto the 'Configuration' page, and change the setting within the 'Roster settings' button at the bottom of the page.