For a DSI, is there a solution to move the brightness selector to the main menu, rather than having to go into a submenu to select the brightness and having to select the main menu again to come out each time?
Good luck doing that without a method of signing it, that path has been blocked quite some time ago. Pretty sure you need to solder some cables to the DSi to even dump the NAND, let alone access the necessary keys. The DSi is far from being "open", it used to be but people ceased working on it due to lack of interest in the platform. Short answer is "no, you can't, unless you really know what you're doing".Well seeing how the Nds is as open as a high school girl on prom night yes BUT you would need to find a un-encrypted copy of the firmware, Mod it with your own code, then re-encrypted, and inject the modded firmware into the nand.
If you are going to play a DS/i game from a flash cart or with an AR, Codebreaker then there is a universal code to adjust brightness in-game.
Backlight Code
DS Lite Backlight Control
*Note: Hold L+R+SELECT then press UP to increase brightness
or DOWN to decrease brightness
94000130 FCFB0000
023FE074 012FFF11
E0000000 000000A8
E28F0001 E12FFF10
A21AB5F0 88234C24
80138811 D02A428B
25803490 F0002000
1C06F82A F0002004
2703F826 21404007
D003420B 420B2180
E018D00C 4231210C
2F03D006 1C79D013
F0002004 E00EF816
E0094331 438E210C
2F001C31 1E79D004
F0002004 E002F80A
F0002000 BCF0F806
4718BC08 30800000
88222100 D1FC422A
80224A08 88208060
D1FC4228 80220C12
88228061 D1FC422A
21FF8860 47704008
04000130 80028802
023FE074 E3520003
D2000000 00000000
Good luck doing that without a method of signing it, that path has been blocked quite some time ago. Pretty sure you need to solder some cables to the DSi to even dump the NAND, let alone access the necessary keys. The DSi is far from being "open", it used to be but people ceased working on it due to lack of interest in the platform. Short answer is "no, you can't, unless you really know what you're doing".