The path will look like this:
HKLM\System\CurrentControlSet\Control\Video\{75BBD41E-4F24-4E21-9BDA-12CF2CC445F6}\0000
And the registry keys are we have these ones to store the list of custom modes:
HKR,, DALNonStandardModesBCD, %REG_BINARY%,\
01,84,01,92,00,00,00,60,01,84,02,00,00,00,00,60,01,92,01,92,00,00,00,60,01,92,02,08,00,00,00,60,\
01,92,02,16,00,00,00,60,02,08,02,08,00,00,00,60,02,16,02,24,00,00,00,60,02,24,02,24,00,00,00,60,\
02,24,02,32,00,00,00,60,02,24,02,40,00,00,00,60,02,32,02,24,00,00,00,60,02,40,01,92,00,00,00,60,\
02,40,02,16,00,00,00,60,02,40,02,24,00,00,00,60,02,40,02,32,00,00,00,60,02,40,02,40,00,00,00,60,\
02,40,02,52,00,00,00,60,02,40,02,56,00,00,00,60,02,48,01,92,00,00,00,60,02,48,02,24,00,00,00,60
HKR,, DALNonStandardModesBCD1, %REG_BINARY%,\
02,48,02,40,00,00,00,60,02,48,02,56,00,00,00,60,02,56,01,84,00,00,00,60,02,56,01,92,00,00,00,60,\
02,56,02,08,00,00,00,60,02,56,02,16,00,00,00,60,02,56,02,22,00,00,00,60,02,56,02,24,00,00,00,60,\
02,56,02,30,00,00,00,60,02,56,02,31,00,00,00,60,02,56,02,32,00,00,00,60,02,56,02,39,00,00,00,60,\
02,56,02,40,00,00,00,60,02,56,02,48,00,00,00,60,02,56,02,56,00,00,00,60,02,56,02,88,00,00,00,54,\
02,56,05,12,00,00,00,60,02,64,02,24,00,00,00,60,02,64,02,40,00,00,00,60,02,72,02,24,00,00,00,60
HKR,, DALNonStandardModesBCD2, %REG_BINARY%,\
02,72,02,72,00,00,00,57,02,80,02,10,00,00,00,60,02,80,02,32,00,00,00,60,02,80,02,40,00,00,00,60,\
02,80,02,56,00,00,00,60,02,80,02,80,00,00,00,55,02,88,02,08,00,00,00,60,02,88,02,16,00,00,00,60,\
02,88,02,24,00,00,00,60,02,88,02,40,00,00,00,60,02,88,02,48,00,00,00,60,02,88,02,56,00,00,00,60,\
02,88,02,88,00,00,00,54,02,96,02,24,00,00,00,60,02,96,02,38,00,00,00,60,02,96,02,40,00,00,00,60,\
03,04,02,16,00,00,00,60,03,04,02,24,00,00,00,60,03,04,02,32,00,00,00,60,03,04,02,40,00,00,00,60
And these other ones to store the modeline definition for each mode:
HKR,, DALDTMCRTBCD256X240X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,52,00,00,02,56,00,00,02,72,00,00,00,32,00,00,02,61,00,00,02,40,00,00,02,41,00,00,\
00,03,00,00,05,51,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F7,53
HKR,, DALDTMCRTBCD256X248X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,52,00,00,02,56,00,00,02,72,00,00,00,32,00,00,02,69,00,00,02,48,00,00,02,49,00,00,\
00,03,00,00,05,68,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F7,2A
HKR,, DALDTMCRTBCD256X256X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,52,00,00,02,56,00,00,02,72,00,00,00,32,00,00,02,77,00,00,02,56,00,00,02,57,00,00,\
00,03,00,00,05,86,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F7,00
HKR,, DALDTMCRTBCD256X288X0X54, %REG_BINARY%,\
00,00,00,0C,00,00,03,52,00,00,02,56,00,00,02,72,00,00,00,32,00,00,03,09,00,00,02,88,00,00,02,89,00,00,\
00,03,00,00,05,87,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F6,9F
HKR,, DALDTMCRTBCD256X512X0X60, %REG_BINARY%,\
00,00,00,0E,00,00,03,52,00,00,02,56,00,00,02,72,00,00,00,32,00,00,05,55,00,00,05,12,00,00,05,14,00,00,\
00,05,00,00,05,86,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F3,E5
HKR,, DALDTMCRTBCD264X224X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,60,00,00,02,64,00,00,02,80,00,00,00,32,00,00,02,61,00,00,02,24,00,00,02,33,00,00,\
00,03,00,00,05,63,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F7,47
HKR,, DALDTMCRTBCD264X240X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,60,00,00,02,64,00,00,02,80,00,00,00,32,00,00,02,61,00,00,02,40,00,00,02,41,00,00,\
00,03,00,00,05,63,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F7,2F
HKR,, DALDTMCRTBCD272X224X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,68,00,00,02,72,00,00,02,88,00,00,00,32,00,00,02,61,00,00,02,24,00,00,02,33,00,00,\
00,03,00,00,05,76,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F7,22
HKR,, DALDTMCRTBCD272X272X0X57, %REG_BINARY%,\
00,00,00,0C,00,00,03,68,00,00,02,72,00,00,02,88,00,00,00,32,00,00,02,93,00,00,02,72,00,00,02,73,00,00,\
00,03,00,00,06,13,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F6,85
HKR,, DALDTMCRTBCD280X210X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,76,00,00,02,80,00,00,02,96,00,00,00,32,00,00,02,61,00,00,02,10,00,00,02,27,00,00,\
00,03,00,00,05,89,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F7,11
HKR,, DALDTMCRTBCD280X232X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,76,00,00,02,80,00,00,02,96,00,00,00,32,00,00,02,61,00,00,02,32,00,00,02,37,00,00,\
00,03,00,00,05,89,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F6,F1
HKR,, DALDTMCRTBCD280X240X0X60, %REG_BINARY%,\
00,00,00,0C,00,00,03,76,00,00,02,80,00,00,02,96,00,00,00,32,00,00,02,61,00,00,02,40,00,00,02,41,00,00,\
00,03,00,00,05,89,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,F6,E5
Built in modes are not defined here, you can get a list of them by calling the specific api. However, you can restrict any of them by the use of this other key:
HKR,, DALRestrictedModesBCD, %REG_BINARY%,\
03,20,02,00,00,00,00,00,03,20,02,40,00,00,00,00,04,00,03,00,00,00,00,00,05,12,03,84,00,00,00,00,\
06,40,04,00,00,00,00,00,08,00,06,00,00,00,00,00,10,24,07,68,00,00,00,00,11,52,08,64,00,00,00,00,\
12,80,10,24,00,00,00,00,16,00,12,00,00,00,00,00,17,92,13,44,00,00,00,00,18,00,14,40,00,00,00,00,\
19,20,10,80,00,00,00,00,19,20,12,00,00,00,00,00,19,20,14,40,00,00,00,00,20,48,15,36,00,00,00,00