Wikipedia says the YS100 is the same as the YS200 except it has no aftertouch and no sequencer.
So I think the number of modulator operators is 0 to 3 and is dependent on the algorithm and brightness affects all of the modulators in that algorithm leaving the carrier operators alone.
Each of the 4 operators has a collection of wave forms to choose from so I also think that is what it is changing.
I originally didn't think much of this synth, but after getting into writing the editor I discovered that it was really interesting especially when you layer the patches on top of each other.
Check this track out. Don't loose patience with the first part. It is worth listening to the whole track (and Part II if you are keen)
If you didn't see the link on top of the page I suggested from my web site there is a new version of the program.
This can run with or without a BC just using a PC and a midi interface.
There is also a second page of the editor that enables you to set up splits and layers.