I have read the first link you provided already. And 2nd link doesn't seem to be relevant for 7.31 AEX single stack.
Moreover, I know there is option User Defined Message Search where we can pre-define the attributes for required interface to have the message search enabled.
But here I am referring to Central PI Message Search which is accessible from SOLMAN and which offers the option to search messages based on pre-defined attributes or custom attributes. I am trying to use custom attribute to fetch the messages. But its not giving any result.
Below are screen shots for navigation:
Thanks,
Vertika