I looked for this information but I can't seem to find it.

I have an existing ROS X86 install that I want to replace the motherboard cpu and ram in.

Can you do this without reinstalling and paying for another ROS license?

Thanks for your time,

You can stick that hard drive into any other machine and it will just work (as long as the hardware is supported by the built in drivers).

i would do this - assemble new PC, get some USB stick and install RouterOS on it (without the license) and see how it works (for 24h uptime) if it looks ok, move your drive to new hardware and check how it works with your current install.

remember, countdown only goes when router is up