How do dynamically substitute a custom popup message for the out-of-the-box popup message displayed

Hi,

Would appreciate any help you can offer to assist me in implementing the following customer requirement in Siebel IP15.9 (OpenUI client):

 

Requirement:  The original functional requirement is as follows:  When the user completes the OPA interview in the OPA iFrame and closes the iFrame popup applet, Siebel should automatically navigate the user to a specific/target view (TAR Submittal View).  When the user clicks the “X” to close the OPA iFrame popup applet, the client wants a custom warning message displayed to the user.  This custom message is different than the vanilla/out-of-the-box one that displays when popup applets are closed.