Change Preferred Server in WinPE (without rebooting)

Hello,

is there anyone out there, who can tell me, if there is a possibility to change the Preferred Server in WinPE without rebooting the client?

I found, that there is a environment variable called "LDMS_PREFERRED_SERVER". But changing it through registry (HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Session Manager\Environment) or set.exe does not work. I could not find a preferredserver.dat either.

Any ideas if this is possible?