Can I replace the SSD in a mid-2014 rMBP?
can i replace the 128GB SSD i have in a macbook pro retina 13.3" mid-2014 with a 256GB SSD from a Macbook Air 13.3" early 2014?
So far Apple does not have a definitive guide on what SSD's are transferable between the systems.
Apple has released different SSD firmware so while it maybe the exact same SSD unit the firmware on it may not play well with your system.
Even though both are PCIe drives the number of lanes is also factor in here. Some systems only have two and others four, all are M.2 blades.
I would wait until either: