Well I guess I will continue in light (no pun intended) that someone might want to do this! The safe way of doing wiring mods when it comes to possible feedback to switches and modules is to use a diode. In case you don't know what a diode does, it only allows current to go in one direction. So here is a diagram to show what to do...
First you can cut this wire any where in the circuit so either as I show here or further up the line to the cargo light. The other two (exterior mirror) are puddle lights, if you have them, they are little lights under the mirror that come on when you open the door. If you have them this mod will not affect them as with it not affect the cargo light or interior lights from working as they do now.
Next where you cut the wire you solder in a diode. Notice I put a little arrow on the diode that is the direction current can pass. so it is important to have it pointed at the switch side and not the BCM.
Now splice a wire between the diode and the rocker (or what ever switch you want) and then attach it to one pole of the switch.
Last you get a power + ( constant) supply wire and attach it to the other pole of the switch. Of course make sure you tape any and all solder and spice joints.
There you have it! the switch will turn on the cargo light ( and puddles) and not the interior lights! since you got a constant + you don't have to have the key on. Now turn the switch off and open the door and the cargo light, puddle and interior lights will come on. Close the door and in a few seconds they will all go off. Last try the OEM switch as you always had to and you will see it works just like it always did!