Salary defaulting using auto complete rule

I have rule configured in auto complete saying Defaulting Salary basis based on Bargaining Unit. But this rule is useful only in Given that salary defaulting occurs only during a salary creation (such as the first time you visit the salary section) and not for subsequent visits OR during a correction.

So submitted another use case - Defaulting Salary basis based on Bargaining Unit on Add assignment, Change assignment. when we Do change assignment from responsive UI, EE old assignment is from 1 bargaining unit and now new is from 2 Bargaining unit, system should default salary basis based on new bargaining unit.