Yes, definitely keep trying until you get someone who isn't locked into that mindset. Because...quite frankly, even though the grouchy CM has worked in tickets for 35 years, she is
wrong!

I mean, let me clarify - she may not be wrong in that they don't allow it. Perhaps DLR does not allow it
now. (Remember I told you the last time I did a swap in October of last year, the CM at the ticket booth - while very pleasant and nice - said she had to check with the supervisor because they aren't supposed to allow it.) Maybe they finally decided to stop allowing it once and for all, but this CM you spoke to seemed unwilling to even check with the DL Bank to see if it was ever accepted in the first place! Clearly it was. I did it on two separate occasions - once for an AP and once for 3 Park Hoppers.
Now there may be allowances because of the kinds of tickets I had, which had no expiration dates on them as well as being unused, and they were not discounted tickets. They were full price. Perhaps combining the GAD and the LMT tickets together would not be allowed. But this CM you reached on the phone seemed like she didn't want to acknowledge that it had ever been done with any kinds of tickets. It doesn't hurt DLR in any way to do a swap with one day/one park tickets - they aren't losing any money at all. But the rules for the GAD or LMT tickets may be different.
I remember that one of the CMs I got on the phone last year told me that some CMs are aware of certain things DLR is allowed to do or not do, and other CMs have no idea that certain things are allowed or not allowed. So it's entirely possible that this 35-year CM has no clue they can do such a thing because she's never personally had to do it for a customer, OR it's possible that DLR no longer allows a swap and the CM just doesn't know that it was ever allowed it in the past.
I wish I could recall the name of the CM I spoke to who helped me on the phone and took the time to check with the Bank. I may have put her name in my TR somewhere. Why do I think it was Janelle? Something with a 'J,' I think. I'll have to check my TR from last year and see if I can find her name when I have time. If I can think of the CM's name, maybe you could even ask for her specifically.