Reverting a task will not help you stay under your limit. Unfortunately, reversing an edit does not reverse the server processing costs associated with processing that task. It simply re-uploads the backup image that was produced by the task. Backups are stored for a specified amount of time depending on the Bulk Image Edit app plan you are subscribed to.
It is recommended to practice with one image at a time (filter by filename), or with a very small collection, before applying that transformation to a large number of images. This will allow you to practice or test transformations without using up a substantial number of credits.