Bumping this thread with updated info. I have 5-day Park Hoppers for the entire family of 5. We just came back from a weekend trip where we used two days. Was on a time-crunch, so left the line for ticket booth after a CM tending the lines mentioned tix can be upgraded by DL app when I asked him if there were other alternatives to waiting in line. He didn't ask and I didn't mention to him that these were bought from LMT.
While walking out, I tried to access the DL app but it was the day when the app glitched for about an hour. Once home, I was able to login again and got the message, "this ticket may be eligible for upgrade to an Annual Pass"... but there was no clickable button other than, "delete this ticket".
Monday afternoon, I called guest services and the CM was not able to resolve after trying a few workarounds. She concluded that it was because the tickets were from an authorized reseller and not direct from Disney. I will have to make a trip back to DL and to a ticket booth to be able to upgrade my tickets to a Flex Annual Pass. :-(