There are many Korean communities in the Mountains north of the Yalu.
So a different 1895 Japanese/Chinese War and you end up with something like this for Korea.
[Yellow line -- rough]
DQ's got a habit of saying what I was going to say. Especially since, in OTL, Japan eventually ends up with both Choson and Manchuko, the DPRK/PRC border is much more of contingent than it appears from the modern-day West. I wouldn't say we're looking at a
radical border change by using the Japanese Method(TM), but we could certainly flip Dalian/Dairen and Shenyang. Both cities saw incredible growth during their Russian and Japanese occupation, and given the, um, frowned-upon methods of the Japanese occupiers, one could imagine a scenario in which ethnic Han flee the cities in significant enough numbers such that after Alt-WWII, it makes the most sense to give the towns to Alt-Korea.
If we're talking Future History, I don't see either of those cities flipping, but I could see a North Korea Meltdown scenario in which the countryside between the border and Shenyang fills up with refugees, and China then rids itself of them by ceding the land back to United Korea. That would be a fairly desparate move, though (and thus low-probability), as the current batch of Chinese leaders would be terrified that ceding even an inch of land would legitimize the Tibetan independence movement.