"According to <R13> The only allowable sources of electrical power for a VEX Robotics Competition Robot is any single (1) VEX 7.2V Robot Battery Pack of any type, unless the robot is utilizing the VEX Power Expander, and a single (1) 9V backup battery. Robots utilizing the VEX Power Expander can use a second (2) VEX 7.2V Robot Battery of any type.
Can a y splitter be used off of 9-volt to power the Vex flashlight? Its purely decorative if that make a difference."
I don’t think so. The 9-volt battery is meant to be used as a backup battery for VEXnet, not for powering a flashlight.
As stated in <R13> part c,
“To ensure reliable wireless communication, it is required that all teams connect a ** charged 9V
Backup battery to their VEXnet system using the VEXnet Backup Battery Holder ** (276-2243).”
Therefore, your idea violates <R13> because the battery would not be connected to the Cortex microcontroller.