LOL... Surely, I can't be the "one guy." To answer most of the questions...
Yes, I unintentionally cut the line when the store rep asked me if I wanted another iPhone 6 Plus. Who am I to argue? Would you say, "No, I'll go back to that long line outside the store?"
Yes, the Apple rep didn't know how to do it, so she called on another rep to assist her.
Yes, she navigated through T-Mobile's POS system to verify eligibility of line and EIP plan.
Yes, it's a real T-Mobile EIP.
No, it's not Barclaycard.
No, I didn't do a JUMP!, so I can't tell you how that would work. But, I can assume that with my other JUMP! I did through T-Mobile directly, since it was through Assurant, they would likely mail a return package with the new iPhone 6 Plus.
No, I didn't have to sign up for a new line.
Yes, I only paid $100 down for a 64GB 6 Plus, plus up-front tax.
Yes, because it was an EIP, I had to sell off my iPhone 5s and pay off the EIP balance on my own.
Yes, I verified on T-Mobile that I now have a new EIP of the iPhone 6 Plus with a remaining balance of $750.