[arman4]

is it possible for a molecule to change its shape or chemical structure when exposed to certain amount of magnetic force?

[Enthalpy]

A macroscopic piece of metal is one single molecule since some electrons are delocalized over the whole object.
And, yes, it can change its form, like collapse under the magnetic force. Building a big electromagnet that doesn't collapse is not easy.
Or coils that produce >100T during a few millisecond current pulse. They last for a few pulses, and then you find their pieces stuck in the lab's walls.

Now, if you imagine small molecules, the effects are tiny. In NMR, one tesla orients about 1ppm more of all hydrogen kernels in the favourable direction, as the proton magnetic dipole times the induction is small as compared with the temperature. Lighter electrons have a stronger Bohr's magneton of 0,67K/T so a significant effect would require a big field and low temperatures.

One example is liquid hydrogen
http://en.wikipedia.org/wiki/Hydrogen#Elemental_molecular_forms
http://en.wikipedia.org/wiki/Spin_isomers_of_hydrogen
which contains initially some ortho from its past at room temperature. As the ortho converts to para, the heat evaporates some hydrogen.