can't speak of experience, but personally , that don't sound like a good idea to me.
either you'll get some funky ass effects, where both items conflict , fighting for dominance , so to speak
or one will over power the other instantly , and the second substance will be a waste of money...
i mean , if you have access to both
might as well get enough of both , and make 2 seperate trips with decent dosages....
again , not speaking out of experience with schroom/cacti mix , i'm just guessing here