Spontaneous changes in sexual orientation have been known to occur in stroke victims, and I think that anything the body can do naturally can be triggered/arranged by “supernatural” means.
Anyone can be conditioned to respond to anything, of course, and conditioning can be done via occult methods.
For my money, you’re more likely to pull something like this off by targeting genetics/identity/conditioning than by flinging love/sex spells at people whose type you are not. Aside from “not being their type,” you have who knows how many little issues like pheromones, experiential conditioning, the fact that one gender’s body is quite different from another, social factors (as I’ve said many, many times - stigmatization and mockery of homosexuality is about traumatizing heterosexual males. “Gays” are just a sufficiently small minority that they are considered allowable casualties. But fear conditioning around orientation issues is ALWAYS worse than you think it is for EVERYBODY, no matter what they consciously think about themselves.), etc, etc.
A lot of experimentation’s been done with simple hypnosis with consistently impressive results - but again, you’re conditioning memory, response, identity, associations, etc. Of course, you either need a willing test subject (that damn fear issue again!) or you need to be an A-grade hypnotist. We now know that our DNA is extremely dynamic and there are lots of switches that can be thrown on and off depending on environment and conditioning.
I’ve been keenly interested in this for a while, simply because it seemed to me that changeability of sexual orientation is one of the very best… experiential “tells” for the fictional nature of the samsaric self. In other words, being able to change something society insists is an innate, hard-wired trait that is supposed to be fundamentally definitive of who/what you are would be a sufficiently but not TOO terribly traumatic way of helping a younger magician, for example, understand experientially that “who they are” is a fictional character in video game, and that this character is fully hackable.
Of course, hacking OTHER PEOPLE gets you to understand the even more important and most taboo lesson - the lesson at the heart of the building occult revolution - that YOUR video game is totally separate from everyone else’s, and you are the only character with free will and self-determination.