Replacing MacBook Air SSD with another MacBook Air's SSD What would happen if you were to replace the SSD of your MacBook Air with an SSD directly taken out of another MacBook Air , same generation, same everything. Stock.
It will be as if you swopped Macbooks. It will work perfectly as it was in first Macbook.

Side note:

You can restore your internal "Macintosh HD" hard drive to an external hard drive using Disk Utility in Recovery Mode, then boot from your external drive on ANY Mac. This is ideal if you want to switch between your home Mac and work Mac with only carrying 1 external hard drive which you can even encrypt before it gets lost or stolen. (Enable FileVault in System Preferences before restoring/cloning)