I found the RXP GTN.ini because I want to adjust the VC screen backlighting on a couple of aircraft. 

However, the entries I saw posted in the discussion are not there. Actually, there isn't a whole lot of data there. 

Must entries be manually added in notepad?

Thanks

I believe you're already posting in the dedicated topic about this:

https://www.avsim.com/forums/topic/533064-balancing-vc-and-2d-gtn-screen-brightness/page/3/?tab=comments#comment-4564279

You might want to start reading all the "recommended" posts displaying at the top of the aforementioned topic page. They'll link you directly to the most relevant information as a starting point.