Hi Jennifer, yes, this can be done but you will need to update the settings at the end to allow people to flow through multiple times (if you wanted them to receive the email more than once). If you only wanted them to receive it once, but you wanted to change the criteria altogether, then be sure to leave it set as "can only flow thorugh once".
Also, be sure the campaign is totally done sending before updating the filter, or it can abort the flow of the campaign.