I would like to announce a new enhancement to Missions: You can now 'rerun' a Mission that has been previously archived!
This will allow you to add more Rewards to an existing Mission, while retaining all other aspects of it - including who previously completed it, so they cannot complete it again.
You cannot change any other property of a Mission (title, link URL, size of reward, etc) when you rerun it.
Any previously-archived Mission can be rerun. However a Mission can only be rerun ONCE per day. An exception to this rule is if the previous run of a Mission saw ALL available Rewards claimed - you will be able to be rerun these Missions immediately.
Once a Mission has been rerun, the details of each instance is available from the Mission Completions details page, allowing you to track the number of Rewards/Completions per individual run of the same Mission.