hello Bluewire,
I assume that you wish to record midi song... or is it a midi song which includes style (because you mentioned fill-in)? -I'm just trying to have clear picture of what you're doing. Anyway, although I'm familiar with a process, I don't compose songs by using midi multi-recording.
About dotted notes... Keyboard doesn't really deal with whole, quarter, dotted, etc. notes. The only thing that defines the type of the note is it's duration. Duration of each recorded note can be seen (and changed) in StepEditor.
The duration of each note is measured in PPQ (Parts Per Quarter) "ticks". PPQ values go from 0-1919, which is 1920 ticks in total (that is, there are 1920 ticks between two metronome ticks). And as PPQ name suggests, 1920 ticks is one quarter note. This is is shown in StepEditor as:
0001:0000 =1/4 note (1x1920 ticks)
An eighth note has a duration which is half of quarter note, which is shown in StepEditor as:
0000:0960 =1/8 note (1920/2 ticks)
Or opposite, a half note is shown as two times of quarter note:
0002:0000 =1/2 note (2x1920 ticks)
Now let's take a dotted quarter note for example. It's duration is 1/4+1/8 and so it's defined as:
0001:0960 =1/4 dotted note (1920+960 ticks)
In short, that way we can define the duration for any note. The only limitation is bar size (note duration can't exceed bar).
About half bar fill-in... Sadly, Yamaha keyboards don't have this feature. Means, if we use half bar fill-in, we will be out of bar boundary after fill-in (until next half bar fill-in occurs).
I hope that was of some help.
Bogdan