How to switch linux kernel console after boot process?
It seems that perhaps you don't actually want the console log messages on another device, but are only proposing to redirect them there to stop them from interfering with binary transfers on the primary serial device.
If that is the case, you may be able to solve your problem by dynamically adjusting the console log level.
http://tuxthink.blogspot.com/2012/07/printk-and-console-log-level.html
Suggests that you can do this by writing to a proc node:
echo "6" > /proc/sys/kernel/printkWould set it to 6 in their example. I suspect setting it to 0 or 1 would work for your purposes - if something goes that wrong, your binary transfer is probably failed anyway.
Log entries should still be retrievable by dmesg regardless of this setting.