Safely that is. I have an old JC Higgins 3 speed that I want to convert to a front hub electric wheel. The wheel has 10mm axles and the dropouts on the bike are nominally 9mm. Can they be enlarged using a file and still be strong enough to do the job?
1mm is nothing if it is a steel fork. If it isn't a steel fork, walk away. For front hub motors, stay with moderate power and speed, and use torque arms. If the fork breaks, you are going to hit the ground rather quickly.