I was building a custom cdrom and found that I needed more disk drive
  device nodes but could not create them because I was running out of inodes
  on the ramdisk image.  I found there were a lot of dev nodes in /dev
  that I really did not need but since they were in the MAKEDEV.tmpl I
  could not prevent them from being created (yes, I did find the arch
  dependent MAKEDEV but that does not override enough).  To get around
  the problem I made a small change to etc/Makefile to allow the
  MAKEDEV.tmpl file to be overridden with a custom version.  This allows
  me to change the mix of device nodes created in /dev in the ramdisk
  image.  Is this worth committing?  or could I have done this another
  way?

Do we have precedent for things like this?  I often keep modified
sources and build from that.  For little things on my desktop, I just
have uncommitted changes.  For projects, we import (into cvs typically)
along the vendor branch.  What you are proposing feels like putting
hooks in to keep a separate version of the file but without having it
appear modified in cvs, and the long-term cleanliness of that seems not
so good.  Yet I understand your problem and why your proposed solution
seems to have be good on the local minimum pain scale.