Create an iRule that can search and replace

then you can try to apply this irule to both Virtual Servers

when HTTP_REQUEST 
{
	switch [IP::local_addr clientside] 
	{
        "VIP_1" 
		{
            set server "SERVER1"
        }
        "VIP_2" 
		{
            set server "SERVER2"
        }
	}
	if {[info exists server]} 
	{
        if {[HTTP::header "Content-Length"] ne "" && [HTTP::header "Content-Length"] <= 1048576}
        {
            set content_length [HTTP::header "Content-Length"]
	    } 
	    else 
	    {
		    set content_length 1048576
	    }
    }
    if { $content_length > 0} 
    {
        HTTP::collect $content_length
    }
}

when HTTP_REQUEST_DATA 
{
	if {[info exists server]} 
	{
		set payload [HTTP::payload]
	    set new_header "<soapenv:Header><job:roleIdentifier>$server</job:roleIdentifier></soapenv:Header>"
	    regsub {<soapenv:Header/>} $payload $new_header payload
	    HTTP::payload replace 0 [string length [HTTP::payload]] $payload
	}
}