Yes, they're placed into a duct/shell and can be removed and replaced because the engines have a set number of hours they can run. Also if newer engines are dev

Yes, they're placed into a duct/shell and can be removed and replaced because the engines have a set number of hours they can run. Also if newer engines are developed they can be swapped (Thanks for /r/justrolledintotheshop) - I recall the cost to replace around $16 million, don't hold me to that though.