Is there a way to change Target Display Mode's default brightness?

[Sunshoopa]

I'm using Target Display Mode on my 2009 27" iMac with my gaming PC so I can play games on the iMac's display. It works perfectly other than that the brightness is maxed even though it's all the way down on MacOS. I have to turn down the brightness 8 notches every time I connect with TDM, which isn't terrible, but is annoying.

Does anyone know if there's a way to change the default brightness of TDM? Be it a hidden file or otherwise. I'm not even sure where the TDM files are located to even attempt to find a way.

I was also thinking of a keyboard shortcut or a script to press the brightness button a few times, but I have no idea if that would work with how TDM works.

 

[discoHR]

Same problem with 27" iMac 2010. I have to turn down brightness 8 notches every time TDM is activated. On some devices (XRGB-mini through active HDMI to DisplayPort converter) it even doesn't allow adjusting brightness, it's full on no matter what.

Looking for a software solution which would freeze iMac's brightness to 50% no matter what iMac sets it to when TDM is activated.