Just thought I'd revive this to add that with the 2016 models, the rear cargo light is now located on the hatch itself AND it is fused with the remainder of the interior lighting. So removing the "roof" fuse disables the circuit. No need to disconnect the battery.
I'm looking at the Manual for a CX-5 2016 model. Is the fuse that needs taken out listed as "ROOM" in the description? And is fuse 54 in the fuse box? It says the the protected component is "Overhead Light" so I'm assuming this is correct. Also how are you sure that the cargo light is fuse protected now?
Thanks for the info! Kinda a newb with this stuff.