Let's say an internet provider (ex: Comcast, At&t, Verizon) says to their users: Hey we have this new free internet access, however, by using it the end ad content will be changed to our liking -for example they can change Ad Units to show their ads or inject ads into content.
What are the legal repercussions here? If the end user's agree, can sites that serve ads (ex: Google Adsense) sue you for replacing their content?
Also wondering about any other issues that can arise from such action.