Thanks for posting about this. It sounds like you are working on an Automation campaigan. At this time you can add new emails as the last step to an Autoresponder series without stopping the series but you couldn't add a middle step until you deactivated the series. As long as no one is queued up this isn't a problem and you can re-start it right away.
Can you give me an example of a campaign that can't be added? Any email should be available to you!
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