You are able to un-initiate a Campaign, this can be done on the Detail tab within a Campaign. There is one condition however which is very important...

You are only allowed to un-initiate a campaign if it has not started sending.

You may want to do this because a mistake has been found and you need to change it. If you do this fast enough then you are in luck. Customers who initiate Campaigns for the future will benefit from this the most. The time window will be longer before it starts sending.