Add new parent level to Account Hierarchy

Hello

Does anyone have experience adding a high level parent on Account Hierarchy?

We have Account Hierarchy defined and been using it for years.

We need to add a higher level to the current top level and all value in current parent level will be child under the new parent that we would like to add.

Please could you advise if there are any thing that we need to aware of, any restriction and any spefic areas that we need to test?

Thank you.