[masklinn]

Individual airliner airframes don't normally get re-engined.

Re-engining is a medium program requiring recertification (as lots of ancillary components need to be replaced to match, and the physical properties of the plane almost always change e.g. shape, size, and weight will change the plane aerodynamics), hence they generally include minor frame updates (e.g. A320neo), but can also require pretty major redesigns (737-NG, 737-MAX).

Plus it's common for the engine to be customised to the frame e.g. the CFM LEAP 1A is the variant for the A320 neo, the 1B for the 737 MAX, and the 1C for the COMAC C919. Similarly, the A220, A320neo, Embraer E2 and Irkut C21 all use different models of the PW1000G family.

[coredog64]

Boeing had a patent 20-ish years ago for making engine interchange simpler on models that were certified for multiple engines. IIRC, it was originally implemented for 757 and 767. Might have been part of DCAC/MRM, but I’m not 100% on that bit.

[masklinn]

But that would be for existing engine options yeah?

As in switching an A320neo from P&W to CFM, not switching an A320 to a LEAP that’s never been an engine option.