And is that as straightforward as it sounds?
Yes the blade is held in place by the plastic cover compressing a spring in a steel collar inside the hole in the blade. The plastic cover just twists anti clockwise into it. The only issue you might have is if the shape of the blade at the case end with the hole is a slightly different shape to the original blade.
There is another type of fitting for the blade that has a drift pin holding the blade in place. Im not sure which type yours is on the granturismo but both methods are fairly easy to do.
Having said that as far as i know key cutters take the blade out to cut it so im sure one would do it for you if you asked or if you wanted to have the new blade cut and still keep the original spare minus the inner electronics in tact.
Search flip key repair or blade change on you tube im sure there will be a few how to guides on there.