iRule to replace http with https for specific URLs

So just to be clear, when the response payload contains this string:

http://user.example.net/images

You want to replace it with:

https://user.example.net/images

And you have an HTTPS (port 443) VIP ready to receive this request? Or perhaps the opposite - you have a port 443 VIP that must change "http://" references in the response payload to "https://", except for "/jwp", which is accessible via a port 80 HTTP VIP?

I tried the following iRule, but it did not seem to work.

you already remove Accept-Encoding HTTP request header, don't you?

Try something like this:

when HTTP_RESPONSE {
  STREAM::disable
  set strexp ""
  if { [HTTP::header Content-Type] matches_glob "text/*ml" } {
    append strexp "@http://user.example.net/images@@"
    append strexp "@http://user.example.net/port@@"    
  }
  if { $strexp ne "" } {
    STREAM::expression $strexp
    STREAM::enable
  }
  if { [HTTP::header exists "Location"] } {
    if { [HTTP::header "Location"] starts_with "http://" } {
      HTTP::replace "Location" [string map "http:// https://" [HTTP::header "Location"]]
    }
  }
}
when STREAM_MATCHED {
  switch -glob [string tolower [STREAM::match]] {
    "http://user.example.net/images" { STREAM::replace "https://user.example.net/images" }
    "http://user.example.net/port" { STREAM::replace "https://user.example.net/port" }
  }
}

I just tested your iRule on an 11.x box and it looks okay. Minor cosmetic modification:

when HTTP_REQUEST {
    STREAM::disable
} 
when HTTP_RESPONSE {
    if { [HTTP::header Content-Type] contains "text" }{
        set find_url1 "http://user.example.net/images"
        set replace_url1 "https://user.example.net/images"
        set find_url2 "http://user.example.net/port"
        set replace_url2 "https://user.example.net/port"
        STREAM::expression "@$find_url1@$replace_url1@ @$find_url2@$replace_url2@"
        STREAM::enable
    } 
}

It changed all references to "http://user.example.net/images" and "http://user.example.net/port" to HTTPS URLs.

And the "/jwp" URL is embedded in the same page and will also be accessible via the same VIP

I don't believe this is true though. An http:// URL will not pass through a 443 VIP.