Yes, the same Change Auditor licenses can be used for each Coordinator in each of the new Forests. Customers may need to have the number of "Seats" contained in the license keys adjusted by your Sales representative in order to account for the new Active Directory objects that could be potentially monitored.
The "Seats licensed" and "Seats used" can be viewed in the Change Auditor Client by going to Help | About | Licenses tab.
Note: All coordinators installed to the same Installation name need to have all purchased licenses applied.