I followed your outline and there a few issues.
After I duplicate the EldergleamAanctuaryWorld and change the name to DragonbornsAntreWorld and I change the name in the Name box to the same and changed to None in the Encounter Zone and Location boxes I then clicked OK.
However, in the Cell View dropdown I only see EldergleamSanctuaryWorldCOPY0000, not DragonbornsAntreWorld.
In the various cells in the world there is a column that has a name, like EldergleamSanctuaryEntrance, where I changed those to NONE. In the cell where loc 29,-6 is located I changed it from Wilderness to DragonbornsAntreEntrance.
I then saved the file (DragonbornsAntre.esp).
I then went to the opening screen of Skyrim and consoled coc DragonbornsAntre and nothing happened.
So I went back to the Cell View and noticed that under Interiors the DragonBornsAntre cell is not listed like other esp files would be.
I have no idea why the dropdown list used the old name of the world before I supposedly renamed it to DragonbornsAntreWorld and instead used EldergleamSanctuaryWorldCOPY0000
So, I am still missing something here. I would have thought that I at least could have consoled into the cell (World?) and walked around or something.
Any ideas where I may have went wrong?
Thanks again for your help!
B
EDIT
I reloaded Skyrim.esm and the DragonbornsAntreWorld selection showed up in the Cell View. However I can't coc to DragonbornsAntreWorld. So I tried to coc to DragonbornsAntre, which I renamed from Wilderness and I was able to get into the cell. However I only got into that one cell and the rest of the cave wasn't rendered.
So I am getting close, just missing something.