Changing the host name, part of the URI and then redirect

I'm fairly new to string map so my apologies if this isn't the right solution.

when HTTP_REQUEST {
  if { [string tolower [HTTP::host]] contains "acb.com" } {
     if { [string tolower [HTTP::uri]] starts_with "/se" } {
          HTTP::redirect "http://www.xyz.com[string map {/se /sv} [HTTP::uri]]" 
     }
   }
}

This will replace any instance of /se with /sv if both the host and uri conditions are met so it should almost certainly be more specific using "range" as you did. I'm going to quick read up on range and will hopefully update it accordingly.