That's exactly what Chinese ISPs have been doing. They occasionally insert an HTML snippet to HTTP responses to create pop-up ads.
(Scanning the data is done on government level so I won't even bother to mention it)
(Scanning the data is done on government level so I won't even bother to mention it)
The survey might have been a DNS redirect instead as by the time I noticed I had already navigated away from the original page and that was one of my few machines that can sometimes use my ISP's DNS. The emergency message test was HTML/Javascript directly injected into a random non-encrypted page I had loaded.