You can't control what spin a particle assumes afaik (edit: I have no idea if you actually can do this). It comes out either spin up or spin down with equal probability and you have no way of controlling this. You can control what kinds of spins are allowed to exit a detector, but this doesn't change the fact that the particle assumed that particular spin in the first place.
Even if you could change the spin by forcing it, you'd be breaking the entanglement anyway.
These types of experiments are often conducted with the spin controlled and the measuring devices rotated to see the effects, especially the effects when 2 matching particles are detected. See http://arxiv.org/PS_cache/quant-ph/pdf/0205/0205171v1.pdf" [Broken] as an example of preparing entangled spin up particles (photons in this case).
Last edited by a moderator: