Short answer: by restarting the server's VDR.
Long answer: at it's current state VDR is not designed to be networked,
so this is not really possible to achieve. Even if you restart the server's
VDR, it will read the new timers.conf, but still _both_ instances of VDR
will record timers that have a priority above the highest "primary limit".
You could write a script, which reads the timers from your VDR-boxes by
SVDRP, checks how to distribute them on the ressources of your machines
and delete/set the necessarry timers by SVDRP.