Recently we bought a second mondeo for my wife. It came with the standard flat key, however my wife would like the flip keys for her car.

I have seen on line people selling second hand keys (previously cut) with all the electrics inside. Also people selling replacement uncut key shells (no electrics).

Am I right in thinking that I could buy 2 second hand keys, 2 uncut shells. Get the uncut shells cut and swap the electrics into the newly cut shells. and move the small transponder chip (the one in the small glass vile) from the existing key into the new shell and reprogram in the the car. to end up with 2 flip keys that will work.

if you have two glass chip then you should be able do it.☺️

The transponder chips are the important part everything else is superfluous.
Just buy complete new keys and swap the chips, takes a couple of minutes to program the central locking to accept the new circuit boards.
Be aware that some key cutters won't do aftermarket keys as they reckon the blades are too hard and can ruin their expensive cutting blades.

Sent from my SM-G965F (S9+)