Update Header text of PR through Interface

Hi Experts,

I person a request to update the Header substance of PR (as highlighted successful the Image) done Incoming Idoc.

In the incoming Idoc, if the PR is rejected connected 3rd enactment application, they volition adhd the Rejection Comments erstwhile rejecting, that rejection comments should beryllium updated present successful the PR header text. 

Is that possible. I cognize that these Header substance present does not get straight stored successful immoderate array and we work that substance utilizing the FM READ_TEXT, but  successful this case, I privation to update that utilizing an Incoming IDOC field. Is that possible.

Help Greatly appreciated.