Well, do this: Set up your universe, and then leave things alone instead of "re-inventing the wheel" every show. Documentation is KEY and critical, even if you have to augment with label tape and a Sharpie, which is almost aways a good idea. Another is a printed charge in a plastic sheet protector, letting anyone know what is what.
You can MOVE fixtures in myDMX. In the Universe set-up, you can drag fixtures around. The programming will follow to the new channel(s). I have tested this multiple times and trusted my BIG show to this, so I can stand behind it and say "this works".
MyDMX does not want "non-like" fixtures to share the same channel. As you can see, this isn't a good idea. It CAN be done. I have a hard time doubling up on Par38's, since I put 2 Par38's per dimmer channel. I am skipping some small step.
Since dimmers DO NOT illuminate, there's still no valid reason to put dimmers in MyDMX. You want to add the fixtures hanging off the dimmers.