Ok, you're kind of mixing a few things. Take locals and the 118 Satellite out of the equation, and there isn't a difference in either ARC, you can watch HBO or TNT or whatever no matter what your system is tagged on any Dish satellite it's on.
The reason they might not have allowed you to get the Eastern ARC, is now adding locals back into the equation, your locals probably aren't on the Eastern ARC. And Dish usually tries not to do mixed ARC'S though they will if it fixes a problem. In your case it wouldn't have for locals I'm guessing? Did the Eastern ARC give you your locals in HD?
The other thing about tagging, you can't add programming if Dish doesn't see that you have the correct satellite. So when I wanted EuroNews some time back, though it was on the Eastern Arc, dish policy was you had to have 118. So to overcome that, the DIRT CSR told the computer I had 118, and poof - I got EuroNews off the Eastern ARC. (I since had to actually get 118 as that channel and TVJapan are now only on 118 for CONUS)