brifters, or just brakes....I don't have brifters, So I wouldn't know about those, but assuming they work the way almost all brake levers attach, you shouldn't have any problem with just tightening the screws a bit more till it is tight. the clamps will form around the bar into the new diameter. They need to be able to because a lot of drop bars don't stay perfectly circular when the curve. If you want to put them back onto a 23.4 mm, you will have to widen the clamp with pliers or something similar until it will fit again.