Without knowing how detailed your understanding and knowledge is of Sleepy's content, but the name of the game is "DOMINATION" when it comes to Sleepygimp content. Firstly Sleepy's comics keep things realistic (to a point) in that all the shit that happens, could happen in the real world, hence Evie and Violet's primary weapon is drugs to incapacitate their victims or reduce them to a defenseless piece of meat for them to ravage. The witch stuff you pointed out has only ever been "alluded" to, never being fully proven thus far. There are hints of Aunt/Lady Carmilla being more then she appears but nothing has been set or proven, just alluded to. Obviously for the plot points, Sleepy makes Carmilla, Evie and Selene's hypnotism far more powerful then that sort of shit can be in real life.
But Body swapping or possession, which appears to be your kink, is something I cannot see Sleepy ever doing as that takes away the aspect of Domination which Sleepy features time and time again. Take for example Evie's chemical compound that removes inhibitions on its victim, that makes Violet not care that the Putz was going down on her or made Nancy's aunt fuck Nancy after they both inhaled the chemical. It is all about dominating the person to do what you want to them or have them do what you want. That is Sleepy's bread and butter and has been since day one.
If you are looking for body swapping or possession, you are shit out of luck and are in the wrong neighborhood for that.