It was suggested that I post the BCL flashing instructions here as well as them being inside BCL itself in the Setup tab.
If you follow these steps EXACTLY as they are written, you WILL be successful in flashing your Grbl hex file!
1. Start up BenCutLaser.
2. Click Setup tab.
3. Un-plug USB cable from PC and plug in again -- or -- just plug it in if it's not connected (key step here).
4. DO NOT click the Connect button.
5. Select correct COM Port.
6. Select correct CPU. Note correct Grbl file will auto-load in textbox.
7. Browse for the Grbl Hex file if needed (inside the BenCutLaser folder)
8. Click the Flash Controller Board button to start the process.
9. A command line window will open and display the progress.
10. WAIT FOR THE PROCESS TO FINISH, then close the cmd window.
Connect to your laser machine and verify the new Grbl version is installed. This is done by looking for the Grbl welcome message that is returned upon a successful connection. The Grbl version will display as part of the welcome message.
UPDATE: If you do this modification, you can also unleash the full power potential of your laser diode. As shown in the attachment, on the Setup tab of BCL, set the "Max laser power value" to 1000. Normally, the maximum laser power value is 255 but if you are using Grbl 0.9i or 0.9j and have done this PWM modification, you set the laser power to 1000.