The legality of adding a change-over switch to a fused disconnect box depends on the specific electrical code requirements in your jurisdiction. However, generally speaking, it is permissible to add a change-over switch to a fused disconnect box if the following conditions are met: The change-over switch is rated for the same voltage and amperage as the fused disconnect box. The change-over switch is installed in a manner that complies with the electrical code requirements for the installation of switches. The change-over switch is properly labeled to indicate its function. The change-over switch is installed in a location that is accessible to authorized personnel.It is important to consult with a qualified electrician to ensure that the change-over switch is installed in a safe and code-compliant manner. Flag for review