How to switch eggs with chicks under a broody hen

Okay so yesterday evening I found out that my hen that I hatched out last spring (cross between a golden sex ling and unknown red and black rooster) has been stashing about a dozen eggs in a small box in the corner of a storage shed. I have absolutely no clue how in the world she found that box, anyways it's getting a bit chilly outside and in three weeks the time it will take for the eggs to hatch, it will be far to cold for newborn chicks. So it's only been about 16 hours she has been on the nest so will she take the chicks this early if I switch all of the eggs out for a couple of chicks? If so how can I achieve this?