Usually getting more steam out of an alternator isn't too hard, I understand. There are experts in the field who can rewind/repair/exchange stators here, so it's logical that you would have them too.

With any significant increase in current draw, you would have to upgrade the charge wiring to be safe imo. And no doubt the Z's marginal regulator, which may be stressed beyond it's limit.

I'm no auto electrician, and no doubt your questions are far better answered by Kev, but some years ago I had a Toyota alternator upgraded and the above mods applied.

All I can say is you must be a legend to be able to ride out of Finland in winter. +10degC is enough to get most Australians shivering and complaining about the cold. Including me!