Scheduled Process to Autoprovision Role Usage

Summary:

We would like to understand how will the Scheduled process "Autoprovision Roles for All Users" work in the following scenario ?

1. Auto-provision rules currently set on condition as BU to assign roles A, B and C
2. Auto-provision rule changed with the new assignment being D keeping the BU condition the same
3. New Users added via HDL and manual forms are assigned role D only via online auto provision rules.

If we run the Autoprovision Roles for All Users process, what will happen to the role assignments for existing users (with roles A, B and C). Will they retain existing roles and get D in addition to their existing roles due to the rule assignment change or they will only acquire D and lose A, B and C.