I betcha that the regulator (many or most of which are in the CPU for the car or in the alternator itself) dares little if the battery is in the circuit or not.
The battery will act like a great big filter when charging, but less when topped up.
The regulator can only see the voltage for the main buss ( that the battery does connect to) and will maintain it with or without the battery. The new regulators are pretty good and will act faster than the old relay types.
The regulators actually control the current through the field circuit, the higher the field current the more the alternator puts out.
The regulator connect one side to the ground (not at the battery, by the way) and the main buss or very likely the actual terminal at the alternator.
Newer cars have the regulator within the software of the CPU and it senses the voltage at the CPU.
Still it is best to not disconnect the battery as surges and spikes could easily occur especially if the battery is discharged and has a high charge rate.