I believe the "change" spoken of is one's innate being.
One can make changes to their form but it does not change their innate being.
For instance: Man can change his heart by have a pig heart transplant, but is still innately man.
So GOD can change HIS form but does not change HIS innate being.
God did change innately...
Definition of innate. 1 : existing in, belonging to, or determined by factors present in an individual from birth : native, inborn innate behavior. 2 : belonging to the essential nature of something : inherent. 3 : originating in or derived from the mind or the constitution of the intellect rather than from experience.
God innately changed through His Son when He was born of the flesh.
The conundrum goes away by the understanding that God is a Spirit (heart) never changing in that aspect but did change innately concerning the flesh to become by nature a man.
If God did not change in such a way then neither can we be changed through His Son.