SOPA (officially) only addresses foreign sites. So they order removal from DNS servers and interrupt advertising or other funding processes from US based companies. But the ability to change the content on a server that is hosted in another country (I believe, IANAL) is beyond their capability. Someone please correct me if I'm wrong.

Also, the issue between domestic and foreign sites is still a bit vague in regards to SOPA. Supporters claim it only addresses foreign sites but most opponents claim (I think) that domestic sites can also be affected.