I've used my beard trimmer to shave body hair that I no longer wanted on my body and it hasn't been a problem.
The only thing that might happen is you void the warranty but they won't know if you used it for your body hair other than your beard anyway.
It's never been a problem shaving other hair from my body with my beard trimmer but the only thing you want to avoid trimming with the beard trimmer is your hair on your head because I actually burned a beard trimmer out shaving my head before.
But just body hair on the rest of your body it's okay to use the beard trimmer to shave that body hair.