avivsky on "adding tags"

Hi,
How can I add tags or change the category of an old post without it being resent (if that's the rigth word) to my rss subscribers? I added tags to an old post, updated it and it appeared in my google reader (I subscribe to my own blog).
Also, how can I make small changes in the text of old posts wihout having them resent to rss subscribers?
PLease tell me that there's a way to do this...
thanks
Aviv