From the manufacturer's own web site, the Trollbridge 24 allows you to charge two 12-volt batteries from a 12-volt source, and then combine the two 12-volt batteries into one 24-volt bank to power a 24v trolling motor
It does not "charge" anything at 24 volts. It does not "charge" a motor
and the motor powering
are two totally separate operations and configurations and it looks like you won't be charging
anything while using the 24-volt output for the motor running. Motor, not 24v battery.
It is just switching the 12-volt batteries in and out of series/parallel array to make the battery
bank supply 24-volts instead of twelve.
It could not be used with a real 24-volt battery, which is an integral unit that can't be switched around the same way as separate batteries in a bank system. And nol, it wouldn't work well for "but can't I charge the two 12v batteries and then use them to charge the 24v battery?" because 24v is enough to runa 24v motor, but not charge a 24v battery.
As for rewiring alternators and changing output parameters...there's experimenting, and then there's d***ing around. Alternators are wired up for specific voltages and loads for reasons, as are the regulators used in them. Can you repurpose them? Sure. Improve on what the engineers have already designed
them for? Not likely. You can have lots of fun learning
about sparky things, but that's the difference between abstract d***ing around for fun, versus getting a job done.