Irule insert html attribute, APM

Try this

when HTTP_REQUEST {
    set flag 0
    if { [HTTP::method] eq "GET" && "[HTTP::path]" contains "/url_with_POST/"
        } {
        set flag 1
        if { [HTTP::version] eq "1.1" } {
            if { [HTTP::header is_keepalive] } {
                HTTP::header replace "Connection" "Keep-Alive"
            }
            HTTP::version "1.0"
        }
    }
}

when HTTP_RESPONSE {
    if { $flag == 1 } {
        if { [HTTP::header exists "Content-Length"] and [HTTP::header "Content-Length"] <= 1048576 } {
           HTTP::collect [HTTP::header Content-Length]
        } else {
           HTTP::collect 1048576
        }
     }
}

when HTTP_RESPONSE_DATA {
    if { $flag == 1 } {
        set loc [string first {method="POST"} [HTTP::payload]];
        if { $loc > 0 } {
            HTTP::payload replace [expr $loc + 13] 0 { action="" }
        }
    }
    HTTP::release
}