Welcome to the forum! I don't recommend bashing it with a hammer (don't read my tagline haha). If the transmission is still working, try this. Jack the tractor up so you can get some ramps under them. Lower the tractor onto them. Put tractor in highest gear. Soak pistons with penetrant. In time, the pistons will break free due to the penetrant and the steady load put on them by the weight of the ramped tractor. Lastly, make sure the tractor is not pointed downhill so it won't roll away once it is free.
Thanks for joining and enjoy your stay!
Thanks for joining and enjoy your stay!