What is the effect of magnetic fields applied to an entangled pair of particles? Just curious...if we can create a pair of entangled particles and position one of them in a strong magnetic field would it have as a consequence that we can't change the spin of the other because that magnetic force applied to the spin of the first particle affects the possibility of changing the spin of the second particle?
 A: In your question are some nuances which have to be clarified first. 

create a pair of entangled particles

It’s possible to entangle two particles by their spin. The only thing we can’t do is to give the spin a defined orientation, say 40° for the one spin and corresponding 180°+ 40° for the second. 

and position one of them in a strong magnetic field

Since we do not know the orientation of the spin, the strong magnetic field could be (with one infinitesimal probability) orientieren in the same direction as the spin. Nothing changes. In most the cases The spin will be influenced and rotated until it’s parallel to the external field.

that magnetic force applied to the spin of the first particle affects the possibility of changing the spin of the second particle?

Any disturbance of the entangled pair destroy the pairing. For electrons or even photons the collision with air molecules  is enough to destroy the common state of entangled electrons. 

would it have as a consequence that we can't change the spin of the other?

What happens with the one particle happens with the over in the same manner. Any manipulation of the second particle is also possible. And -most important - any manipulation of one particle doesn’t change the spin of the other. 
