The FCC has approved the Lumia 950 XL for sale in the USA. The device has just been submitted for examination on the 15th October, and the official reports have now been published.
The documents, including the user manual, do not reveal much new information, with the user manual looking either to be a quick start guide or a stand-in for a much longer final document.
It does however include the above diagram, which shows how to remove the case of the device (which as can be seen above includes the NFC antenna). The process looks like it may require some dexterity, but then this should ensure a snug, seamless fit for the final product.
See the documents for Lumia 950 XL RM1116 at the FCC here.