Seamless "downgrade" from test-brach to final version

[Arik Raffael Funke <arik funke gmx de>]

Hi,

I will have to set-up a system in the next few days and was wondering 
whether it is possible to "downgrade" from the test version seamlessly 
(i.e. without fresh install) once the final version is out?

Regards,
Arik