It's not just about going through a song-and-dance. It's about making an OS that has different behavior - often very tiny differences, but differences that would make the distro worse for most users.
I wouldn't be surprised if there were still patches required, but at least on the face of it that should get you most of the way there.
Is this actually true? Can you give a real example of where Huawei EulerOS or Inspur K-UX are inferior to their non-certified base (yet another Red Hat Enterprise Linux clone) due to their UNIX certification?
Afaik, EulerOS and other Unix-certified Linux distros just ship the usual GNU userland.