Can we override the probation end date or duration fields?

Summary

Are we able to override the probation end date or duration fields for employees that were temps and become perm and a 'second' probation applies?

Content

The Fusion HCM system either calculates the probation end date based on the duration entered or the duration based on the probation end date entered.  This is great for most hires but we do have situations where an employee is hired on a temporary basis and is not subject to a probationary period.  They are later offered a permanent contract and a probationary period then applies from the date of the permanent role.  We want to be able to create a new assignment record (Manage Employment > Update) and record a probationary period effective from the date of the permament role not