Using version 1.2. I can't seem to find a way to do anything other than add subscriptions, folders and delete subscriptions. Is there any way I can just rename my existing subscriptions?
It is not possible to manage the feeds inside Reeder.app. Nevertheless it will synchronize all changes made to feeds within Google Reader. So if you want to rename a feed, open the webpage of Google Reader and go to the preferences.
In the prefs, choose the Abonnements tab (at least this is the German headline) and rename the feed.
If you now head back to the Reeder.app and synchronize your feeds the changes will be reflected and the feed will be renamed.
Please remember that this workaround will only work until July 1, because Google is shutting down the Reader service.
It isn't possible to edit subscriptions on Reeder. You will need to login to your RSS, or news feed account to edit subscriptions.
Please go ahead and contact their support to request the ability to do that.