I have heard mixed results on how well this works, but the only way to change career track is to demote your Sim with cheats, back to the level where they get a choice of career focus. With Culinary, if I am recalling correctly, you choose when you are promoted from Rank 5 to Rank 6. So demote down to 5, and then earn another promotion. You should have a choice then to take the Mixology career. That is according to a SimGuru a few years back.