We’re registering our child with FIS for the first time. However, we want to change his/her national affiliation with U.S. Ski & Snowboard and FIS, how do we go about doing this?

As long as your child hasn't registered with FIS previously, there is no problem changing countries. To change countries for U.S. Ski & Snowboard, you will need to provide proof of citizenship for the country in question.