#!/bin/bash
s='next: 
    {
     host = "http://n...content-available-to-author-only...e.com/err1.2.2/table/kenny.xml.gz"
    };

second:
   {
     host = "http://n...content-available-to-author-only...e.com/err1.2.2/table/kenny.xml.gz"
    };'
sed  '/second:/{N;N;s#"http://.*"#"next.com"#}' <<< "$s"