That's a new one on me - I fail to see how a filament heated to well over a 1000 degrees C can be less brittle than one which is cold! Years of practical experience has shown me that an operational filament lamp will fail very easily if subjected to vibration or a sudden shock, but you have to be fairly determined to break the filament when it's off. Think of the start up shaking that typically afflicts any piston engined A/C!! Many years ago I had to rubber mount the headlight on a motorcycle of mine as the bulbs, and speedometer were failing with alarming regularity. There might be a case for switching it on once the engine's running, then turning the generator on so that the lamp is not subjected to the maximum voltage in one go.