how to change ItemDetail - ItemType field

Hi All,

I am struggling to update the value for ItemType in Item Details section of SRM UI Add-on sapui5.

I written code in  CUSTOM_PRE_EXIT and  CUSTOM_POST_EXIT as well(just trying) ...but my custom values are over written and getting the actual values from SingleItemDetails.controller.js

code I written

if(controller && controller.getView && controller.getView() && controller.getView().getId() == 'singleitemdet_id'){

if(sap.ui.getCore().byId("ItemType")){

if(sap.ui.getCore().byId("ItemType").getValue() == "Service"){

sap.ui.getCore().byId("ItemType").setValue("XXXXXXXXXX");

}

}

}

this is getting updating only the first time, if I navigate to other screen and come back which is overridden by above sap code, I am sure I am missing some flow and don't know how to call my custom code in CUSTOM_EXIT should after SAP SingleItemDetails.controller.js

Thanks

Rajesh