I have a need to to convert a CSV file that was surveyed in NAD83 Zone 12 to NAD83 Zone 13 coordinates, is there an online tool that can do this for me?
You might try the National Geodetic Survey Coordinate Conversion and Transformation Tool (NCAT). It has a multi-point option and an API as well. I haven't used the API.
When using the single point option, you can override the output UTM zone in the bottom, output portion.