Engine replacement happens on airplanes fairly frequently. You don't want to scrap an airplane because of a single damaged turbine blade, or even keep it on the ground for longer.
Yes but the new parts meet the specs of the original design. The design itself isn't flexible. You can't make the engines significantly bigger without significantly revising the blueprint as a whole. That was the Boeing Max lesson. Just changing the software was not enough.
https://jalopnik.com/how-airlines-decide-to-replace-jet-engi....