While you can freeze cooked sweet potatoes, I do not recommend doing so unless you absolutely have to. The sugar syrup will crystallize when frozen and does not have as nice a texture once thawed and reheated. You can store them in the refrigerator in an airtight container for up to 3 days after preparing. If you do choose to freeze them, do so in a container with 1" extra space at the top and store them for up to 6 weeks.