The metalurgical specs on SS are not far from those of the resistance wire they use to wind
wire wound resistors. and if the cabling is sufficient to carry the full rated amp capacity of the alternator it is not going to heat up by one placing a series resistance in the circuit.
I have also used long, small diameter SS machine thread screws as series resisters or shunts on wind
generators with crimp connectors on the wiring so that the resistance can be adjusted.
Once upon a time high wattage rheostats were easy to source but I have not seen one of those for years.
If you want a manually adjustable current control you can wire an adjustable DC speed controller in parallel but if you go this route
you need to monitor
the battery voltage and manually adjust to keep from damaging the battery.
Of the various means the bike spoke has proven the most practicable as I keep a stock of spares on hand for my bike anyway.