Yep — you can absolutely check out what we do for, e.g., OTA transfers in the firmware code and try to do something similar. You can search the firmware for things like “chunk” and “FileTransfer” and for example look at where we handle the message from the cloud that says an OTA update is about to begin. When you dig in from the hal to the platform check out the code on the Core, since it used the external flash. The Photon and P1 send OTA updates to internal flash.
As mentioned here the interface to the external flash chip is in the SPI flash library.