Making changes to a draft Campaign

It's awesome that I can send out a Campaign Preview through the API, but how can I make a change if needed?  I can't see anything in the API documentation or the documentation for "campaignmonitor/createsend-php" that would allow this. 

Even if I had to delete and create a new one, I need a way to pull the content for the campaign to change.  Is there any way to do this?

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