[Lynn Eades]

It would probably be o.k., But.....
It would be better to polarize a generator every time one is fitted to a vehicle.
This way it has to be right.
If it is not done, and is wrong,(50%chance) what happens is that when the engine stops the cut out contacts in the regulator stay closed.The current from the battery back feeds to the geny which tries to "motor". The geny cannot motor, being held by the fan belt. The net result is that the geny burns out, along with the cut contacts, essentially wrecking the regulator.
For the sake of connecting the live terminal of the battery with a wire, and making it spark on the small terminal (field terminal) of the fitted geny, it saves all the grief.
This is the case when your vehicle is earthed either positive or negative.