The Vreg can't make the alternator produce more power than it is capable of providing. The Vreg's job is simply to keep the battery from overcharging in the conditions that allow the alternator to provide all the bike's usage AND put too much power into the battery. As such, it is just a battery protection device rather than a true regulator of system voltage.
As for VREG trip point, the only trip point of significance is the battery voltage high point. The rest of the voltage points are determined by battery charge state, which will be continually diminishing at idle, as the battery depletes.
If you start changing Vreg settings, you run the risk of hunting for a replacement that has been unmolested, as adjustments on the bike are not straight forward, and if done incorrectly can damage the battery via overcharge.
Good luck!