Hi, I hope you're doing well!
Theoretically speaking, it's possible to add external RAM, because the JN5169's memory map has unassigned address blocks, but the included APIs don’t natively support external RAM. To do this, you would have to implement it yourself. Alternatively, you could try using an external flash or EEPROM memory instead of RAM.
Please let me know if you need more information.
Best regards,
Sebastian