Hyperpixel4 - Disable backlight on shutdown

I have used your trick in the “dual-boot” thing suggested here in this thread: Hyperpixel - selective output (eg on boot)?

I’ve added the dtoverlay string in both config files but when I’m using the HDMI obviously the HyperPixel backlight is still on because it didn’t receive the “shutdown” command. Is there a way I can shutdown the HyperPixel4 or the backlight if I’m using the HDMI output?

Furthermore, is it possible to adjust the brightness, contrast and similar?

Thanks and sorry for all the questions.