Yes, it is possible to convert any HAKKO FG-100 or HAKKO FG-101 to display temperature in either degrees Celsius or degrees Fahrenheit.  This is done by changing the position of the jumper pin on the PCB inside the unit.

NOTE:  The HAKKO FG-100 and HAKKO FG-101 are factory adjusted for accuracy at the time of manufacture and conversion of the display may have an affect on the accuracy of the temperature measurement.  This conversion will also cause potential issues in that the unit will no longer meet the published specification for that particular model number.  Furthermore, any field converted product that is returned for a certificate of calibration will be converted back to the factory specification in order to complete the calibration process.

IMPORTANT:  When opening the Hakko FG-100 to convert the display, be sure to take the necessary ESD precautions and remove the battery from the unit.  Failure to do so may result in damage to the product.