Changing the Hierarchy Structure

Summary:

Client is using around 6 parents and child for account hierarchy. However, client decided to change the hierarchy for one parent and child. So, what are the prerequisites or considerations need to take and how to reconcile the balances as well. Is there any document or steps need to follow on this.

Some of the child values are made as parent values when we try to enter it is throwing some error message. So, what needs to be done for this.

Once I import new values it would be current, and can we have 2 base hierarchies as it becomes history?