For non-tls connections they could. Some examples of isps meddling with unencrypted connections: https://www.eff.org/deeplinks/2014/11/verizon-x-uidh https://

For non-tls connections they could. Some examples of isps meddling with unencrypted connections: https://www.eff.org/deeplinks/2014/11/verizon-x-uidh https://www.eff.org/deeplinks/2014/11/verizon-x-uidh https://thenextweb.com/insights/2017/12/11/comcast-continues-to-inject-its-own-code-into-websites-you-visit/ https://thenextweb.com/insights/2017/12/11/comcast-continues...