Pretty sure either 172, 173, 192, or 193 (don't remember which one) is hardcoded inside gsp ("graphics server process" sysmodule, responsible for initializing the GPU and LCDs), and removing this cap would require a patch to gsp.
This is not a fault of anyone, but is an intended "feature" by Nintendo itself to prevent LED damage by heat stressing it with a high backlight value.
LCD Tweaker values don't stay on new3DS, only on old3DS, and even then it randomly resets like on new3DS, except less often.
Edit: to answer simply:
Yes, it is possible, but someone needs to make a code.ips (which you can just put into a specific folder name in the luma folder on your SD) which patches this limitation in gsp.
After that, any brightness level editor or config block editor should be enough to change all 7 levels (only 5 are used).
maybe you have idea of why i got my both screens so dark and how can i fix it ?
when i ordered it from japan on amazon it says it was new and it came with the original package and looked new it even had the original battery inside.
maybe the battery is bad (lasts about 1.5h -2h of gameplay) ?