Rewrite host and URI, then redirect

That's a good start. You can do pairs of replacements within string map (Click here😞

string map {find1 replace1 find2 replace2} [HTTP::uri]

You don't need the -glob flag on switch if you're not using wildcards in the switch cases. You skip the intermediate variable for $host. And HTTP::uri is cached in the event, so logging it after modifying it won't show the change.

 
 when HTTP_REQUEST {   
    switch [string tolower [HTTP::host]] {   
       "app.domain.com" {   
          log local0. "redirecting to http://www.google.com[string map -nocase {"/path_to_replace" "/new_path" "index.jsp" "index.asp"} [HTTP::uri]]"   
          HTTP::redirect "http://www.google.com[string map -nocase {"/path_to_replace" "/new_path" "index.jsp" "index.asp"} [HTTP::uri]]"   
       }   
    }   
 }   
 

Aaron