@sianella Wow, nice catch. I don't think anyone has commented on that here. And the mole is always on the same spot, below the lower right eyelid.
I think the mole is to help readers tell apart the body with Ee-jae's soul, and how it was with the original owner. Only when Ee-jae is in it is the mole there. In the flashback of this chapter, the original Ji-hyeong didn't have a mole. And I checked that the serial killer had no mole before Ee-jae became the user of his body. I didn't check all the past lives, but I'm pretty confident that's the case.