Hello Rui,
I tend to agree that this will only work with new emails that enter the queue. Once an email is in the queue and awaiting agent assignment I don't think there is much you can do. Without going in and manually rerouting the emails.
Maybe someone with more architect knowledge can help out but I cannot find anything in our dev center or documentation that points this specific feature out.
Cheers,
------------------------------
Cameron Tomlin
Online Community Manager/Moderator
Genesys - Employees
------------------------------