Hmmm I just had a thought. Things that are server-sided. . . Somehow the client has to send information to the server and the server fetches the appropriate specification (Like your client sends to the server that lets say you have a certain gun, and then the client retrieves the specs on the gun, and how it works blah blah blah.) Couldn't you theoretically change what gets sent to the server before it does?
I don't really know what's server sided so I can't think of a good example. I suppose it would be akin to packet editing, except your editing stuff while it is still in your computer before it is sent. I completely lost track of my point though. Carry on.