Will Magnetic Field Changes Cause Orbit Decay?
no.
Thinsats are in a near-circular orbit - eccentricity is less than 6%. Most of the magnetic field change over an orbit happens because the dipole is offset from the rotation axis. The effective McIlwain L shell varies from 1.8 to 2.2 for the 14357 second orbit. The B field is:
B = B_0 ( R_E / R )^3 \sqrt{ 1 + 3 \sin( latitude ) }
B_0 = 30 μTesla. For the equatorial orbit, this simplifies to:
B = B_0 L^{-3}
... so the B field changes from 5.13 μT to 2.82 μT over the course of the orbit, and the delta is ± 1.16 μT