The LCD controller features brightness control in the chapter 8.2.38. Write Display Brightness (51h) of the datasheet: https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf but it is unclear if that works as expected and has the desired effect.
TVs also allow changing brightness/contrast values but this just alters the color values of what is displayed and does not actually change the backlight intensity.
This needs to be evaluated with the AXIOM Remote LCD.
If it does not have the desired effect we can control the backlight LEDs directly from the PIC32. By using PWM we should be able to implement high frequency dimming.
Sheet 3 LED_A1 - LED_A4