Delimit Position Vacancy during PA action

Hi Gurus,

Currently, during PA Action in PA40, a screen will pop up in IT0001 - Org Assignment to delimit Vacancy. In the pop up screen user needs to choose Yes in order to delimit Vacancy. But user don’t choose yes (to delimit Vacancy) which is incorrect, by choosing No the Vacancy in OM will not be delimited. When you go to the structures it appears as like same employee is occupying two different positions at the same time.

Is there a way that I could make the pop up box to strictly allow a user to only select YES, maybe grey-out the NO

1. e.g. Transfer from Position A to Position B (currently Position is vacant because our setting is one position is for one holder only)

Please help!!