You can add extra incentives at any time. Once a reward tier has been added, you can only edit it as long as there’s no reps currently working towards that tier.
Using the previous example, if Reps was live and the top earning rep had 1200 points:
1000 Points Free Queue Jump ticket Cannot be edited (Already awarded)
1500 Points Free drinks Cannot be edited (Reps are actively working towards this tier)
5000 Points Free hoodie Can be edited (No reps are working towards this tier)