Change project and task owning organizations.

Summary:

We have a handful of projects which are linked to an incorrect project and task organization.
Costs have been incurred on these and have been accounted as well.
We wish to change the project organizations to the correct one, using

 "Change Project and Task Organizations process"

What will the impact on the existing costs be ?
Will they be reversed and re-created on the correct organization ? Or will it only impact the costs yet to be processed.