When you add the TCPIPClientInput node to a message flow, you can configure it.
<mcd><Msd>MRM</Msd><Set>DHM4UO906S001</Set><Type>receiptmsg1</Type>
<Fmt>XML</Fmt></mcd>
If you set values, and if they differ from the values in the MQRFH2 header, the values in the MQRFH2 header take precedence.