only suggestions :
if you use the pry bar method, you must tap on the back side of the rim (180 opposite the pry point) to help wiggle the rim off.
have you tried a piece of 2x4 tucked under from the opposite side of the tractor and put up against the back side of the stuck rim... pound on the 2x4 to push the rim off... rotate the tire a bit and pound again... repeat as necessary.
if you must pound on the axle from the front, use a piece of aluminum stock or brass stock between the hammer and the axle... the softer metal transfers the "blow" to the axle, but it deforms instead of mushrooming the axle.
these methods have worked for some, but you must decide how much force you want to apply and are comfortable with.