If you're going to prime condition your kegs with priming sugar and you're only bottling a twelve pack, I would use the normal amount of corn sugar in the bottling bucket (1/2 cup for priming a keg). Then siphon off your 12-pack and keg the rest.
To account for a slightly smaller amount of priming sugar you used (1/2 cup VS 3/4 cup), you'll want to store the bottles in a warmer setting (70-72 degrees) and give it at least three weeks to carb.
If you're going to force carb your keg,,,uh,,,not sure.
1 12-pack is roughly 1/4 of your batch so maybe you could adjust down your priming sugar accordingly (1/4 of 3/4 cup).