To what extent does the karma created by a walk-in spirit affect the future of the prior occupant of that body when they reincarnate?

There will be an influence. There is a kind of energetic entanglement. So what happens during the course of time the walk-in spends in the body, those experiences will be blended into the akashic records of that prior soul, as well as to the akashic records of the arriving walk-in. So this is a kind of a hybridization that takes place. But for the most part, will be advantageous to the prior occupant, given that the newly arriving walk-in will have to work on and hopefully heal at least the big things in order for that body to be useful and to be successful personally, following their arrival. So this will be a benefit for the prior occupant of the body. They will likely be escaping a life that was unfavorable from their perspective, and they will get some help in the bargain to clean up the mess they left. The walk-in has the advantage of not having to go through childhood, albeit with needing to heal any slings and arrows that were experienced by the prior body's owner, the major advantage being, the walk-in is slipping in under the radar, because the greater scrutiny of individuals is done as infants by the interlopers to figure out who they have been in the past and earmark them for extra harassment if seen as a troublemaker potentially. A walk-in inherits the body of someone who has already been scrutinized and branded as unimportant from the perspective of the interlopers, and that confers much greater safety for a high-level lightworker to have a chance to be a contributor again as a physical human.