Replace X axis motor with different model
Since they have the same rotation angle per step, I shouldn't have to calibrate the new model, right? (I'll use the original wheel)


Yes, you do not have to change anything, other than the Vref of the stepper driver.


  Did the vendor send me a motor with inferior performances?


Yes, the one you received has a lower height, so smaller coils and smaller permanent magnets; basically lower torque.


  Will my performances degrade if I use the new motor?


That depends on the loading of the carriage of the X-axis, it could if it is heavy; you now have less torque available to move the carriage. But, this type is frequently found in 3D printer kits and should work.