I've already done this with a Spyderco Endura 4. I bought a green G-10 Endura w/flat grind plain edge blade on eBay a while back. As it turned out, I wasn't happy with the edge grind on this knife (too obtuse). I ended up swapping a combo-edge blade from an FRN handled Endura 4 into the G-10 handle. The other thing you need to make sure to do is to also swap the locking bars of each along with the blades, since they're machined to match & lock up cleanly with that particular blade. If you don't, there will either be too much vertical play (a gap between blade & locking bar), or the blade will hit the locking bar prematurely, preventing full opening.
In this case, the 'body' of the combo-edge blade is beefier (thicker) than the flat-grind blade, but they're equal in thickness at the tang where it mates to the handle. This resulted in a very cozy (snug) fit for the combo blade inside the G-10 handle's liners. And the thinner, flat grind blade all of a sudden looked skinny inside the FRN handle. But they both functioned (open/close/lock) flawlessly after the swap.
Edited to add:
Although swapping blades between these two Enduras was relatively easy due to the lock type (lockback), it could be much more complicated with other locking mechanisms, especially frame locks (the locking mechanism is integral to the handle itself, and machined to lock up solidly with it's own matched blade).
