So I tried listening to the Applejack files again, this time after looping a trancing/susceptibility file for an hour or two. The results are... interesting. No imposition that lasted past the end of the file, visual or tactile, and I don't think my mental processes are going differently. But my immediate mental image of how my head looks has been replaced by how Applejack's head looks. I can still remember how I actually look, and looking in a mirror still shows my actual face, but my first thought when I reach for an image of my head is now "Applejack's head".
Only time will tell if this will last until the morning.