There are so many things that could cause DC voltage to be lower than max when measured at the battery that it is impossible to state that the condition means a bad regulator/rectifier.
The battery is the most likely reason for low voltage measurements. Loose or corroded connections are next on the list. Poorly-wired accessory installations might be the cause. Corrosion at the fuse block is another. So is the very real possibility that there is nothing at all wrong -- 12.17 VDC at idle is not alarming at all from a stock Honda Shadow r/r. It should go up around ~3,000 RPM and maybe even drop at higher revs.
You're relying on a second-rate manual and have a limited understanding of your bike's charging/electrical system or proper diagnostic testing of same.
