Reinstalling the MBR that CTM uses

Is there any way to do that? If not, there should be. I’m asking because I was trying to install my old hard drive back into my PC (along with the SSD I got for Christmas). Somehow the MBR was corrupted while doing so.

We know a way to restore a new MBR (preserving the partition table).
I don’t know a method to backup/restore the changed MBR of CTM.