Yes, you can edit campaign till the campaign is in "Scheduled" Status. 

You can edit the content and modify the settings till your Stage 1 is in Scheduled. The moment Stage 1 is queued (i.e campaign has passed the "Scheduled" status**)**, you won't be able to alter settings of a campaign. 

However you can edit the content (i.e. subject and body of follow-up emails) of the subsequent stage before they are triggered but the settings froze in stage 1 can't be altered.
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