Are Makerbot Smart Extruder nozzles swappable?
Yes, you can change the nozzles with the 5th gen line printers, although it's not recommended or supported by Makerbot. You're on your own if something goes wrong with an aftermarket nozzle. Here's a swap video from Fargo3D: https://youtu.be/vL80bslk9vw

I would recommend "mk8" Makerbot Replicator 1/2/2x style nozzles, since these will be similar dimensions to the original nozzle. Ebay has lots of cheap ones, or P3-d and Micro Swiss are popular options for premium Makerbot mk8 style nozzles. But you should be able to use any standard M6 male thread, ~2mm ID nozzle (such as from E3D, because the Smart Extruder Z homing routine will compensate for nozzle length. 

When you change the nozzle, you're also going to need to change the slicer settings. Do not use default settings with a different nozzle. Smaller nozzles will require significantly lower print speeds, and larger nozzles will require wider extrusion width. You can create a custom profile in Makerbot Desktop to do this, or use a 5th-gen-compatible slicer like Simplify3D.