The answer is yes and no... I know not making much sense, but hold on
The SSD is replaceable, but due to apple being the special kid they have gone with a proprietary connection. In the previous rMBP model the market (OWC) introduced user replaceable SSD, but for now we have not seen any 3rd party parts.
Only the TouchBar models are soldered into the logic board, nTB models like yours can be upgraded, but as @Schranke said, not very easy to find one at the moment and they are way overpriced, but there should be other manufacturers offering them soon.