Astral projection is your Astral body traveling through the planes. It is made of energy vibrations. As such, I believe it might be possible to project that energy to something of lower vibration, such as a body.
As it is possible to communicate thoughts and feelings to another person who is ooutside of the planes, it should be possible to send out harmfull or healing energies. I am positive that this is something Astral beings, such as spirits, demons and other unknowns sometimes do to get in touch with us.