You can edit almost anything about a syndication package after it's been published, it's very flexible.
For example, you can edit the syndication settings and add more groups. When you save, the new groups you added will receive email messages notifying them about the new syndication package they're receiving, and the package will show up in their syndication tab.
You can also edit the email or action template (or remove it entirely and substitute a new one) after the syndication has been sent. Doing this will only affect receiving groups going forward -- groups that have already clicked on the syndication package and set up their drafts will not receive these updates, but groups that haven't yet will.
Finally, you can unpublish your syndication package if you'd like -- doing so will not unpublish or delete any drafts that have been made by receiving groups, but will remove the syndication package from each group's syndications tab.