Would you elaborate on this? What are your examples? Mods are known to update submission titles (in accordance with the guidelines), but I'm unaware of any other content changes they make.
Thanks for clarifying. I read your comment as to mean mods updated the content of comments. All of the items you mention are actions the mods engage in in their role as moderators, which they themselves have described elsewhere.
1. They detach comments from comment threads (to hide them?)
2. They boost some stories so that they remain on the home page for a longer time
3. They also remove some posts from the front page... (because they are duplicates, not "quality" content, etc...)
I could probably come up with more examples, but I'm sure that you get the idea...