When we apply magnetic field to a hydrogen atom such that the Magnetic Lorentz Force acts inwards on the electron, will its radius shrink to a value lesser than the Bohr's radius, because according to Bohr's quantization radius of electron orbit can never be less than Bohr's radius?
In quantum mechanics the electron does not have orbits, only orbitals, probability loci for where the electrons will be if a measurement is attempted. The Bohr model is an averaging out of the underlying quantum mechanical behavior. An average radius can be calculated and that is what may change if a magnetic field is imposed.
There are measurements of atomic orbitals and orbitals that are important in chemical studies. There are calculations of how orbitals change where a change in average radius is taken into account , so yes, the average radius can change by external magnetic fields.