Not really. If someone hands me a newspaper, I am free to cut it, draw on it, tape over it, or anything else I want. The control over the content ends when the HTML with the site content is sent to me. If I want to hand the HTML to someone else to tape over the ads with different ads before I read that content, that is completely within my rights, both in the physical and the digital versions of this analogy. They can paywall the content and they're sure to get paid before I download it, but if they send it to me for no cost then they've chosen to give the content away. Remember: not retrieving advertisement images from a server somewhere is not "theft." Once the content reaches the user's private network, the user has unlimited rights to do with it as they please, excluding any restrictions under copyright law which basically just means they can't redistribute the modifications unless the fair use doctrine applies.