It has nothing to do with a regulator or a cutout relay. Even if you used a generator without either of them(I don't know why you would), polarization is still a good idea any time some part of the electrical/charging system is disconnected, when you install a new generator, or if the generator is not charging the battery.
The polarization that takes place in these generators is to "replace" or "correct" the residual magnetism in the pole shoes, in order to make sure that it will generate the correct polarity to charge the battery.
When the generator is not turning, and the cutout relay disconnects it from the battery, there is still a very small amount of magnetism that will be left in the pole shoes. If this magnetism gets destroyed or reversed(by a knock,or by an erroneous electrical current...) then the generator will either not charge at all, or worse, will charge in reverse polarity, neither of which are what you want...
These generators are "self excited", that is, they use their own output to generate the magnetic field that lets the generator, well, generate...
When the generator first starts turning, there will be a very small amount of magnetism left in the pole shoes, and this will cause the generator to put out a small voltage , part of which is tapped off for the field coils, which increases the magnetic field, which raises the generator output, etc...until the voltage is high enough to kick over the cutout relay, which then connects the generator output to the battery.
To polarize, simply connect a wire,momentarily, between the 2 terminals on the cutout relay. It will spark, and send a momentary current through the field coils, thereby properly magnetizing the pole pieces.
