How to Mass Update One Segment Value in All Employees' Default Expense Accounts?

We are seeking to change one segment of the default expense account for all employees (about 10000). We are doing changes to BSV in COA we are removing existing BSV and adding New BSV so we would like to update all Expense Accounts for employees and If COA have 2( ex 101, 102) BSV if we end date one(101) will BSV will the all code combinations on 101 will it default to 102?