Create a custom warning message on Purchase Order page

Currently when an item from a different org is selected on a purchase order that is for a different Requisitioning BU, an error message is displayed on the Purchase order screen which does not give a correct reason of the error.

Business users might face issues and would not understand the reason for not able to progress the PO, hence would need to have a user friendly message or a custom message that gives a clear understanding of the issue.

Would like to know if we can customize the message.