From the SD5 manual........

"Arrange D/Riff: an accompaniment variation that is more complex than the one of Arrange C. In some cases this Arranger, as already mentioned, acts as Riff, in other words it activates a typical harmonic sequence for
the musical type of style set.

The presence of a Riff is enhanced when you load the style by the fact that the LED of the Arranger D flashes (the LED flashes until it is played for the first time) and also by the symbol (R) on the Display under the name of the style loaded.

Neither Fill-ins nor the Break can be activated while a Riff is being played.

When playing a Riff, the normal acknowledgement method of the chords is altered. The acknowledgement method is determined by the settings of the RIFF KEY function in the INTERACTIVE ARRANGER menu.

Depending on the settings of this function, you can set the harmonic note of the Riff only during the first musical beat (RIFF KEY None mode). In this case, once a Riff has been launched and the initial chord has been acknowledged, the musician can play freely over the whole keyboard in pianist mode or using the Lower's for the left part and the Preset's for the right part.

Alternatively, you can force the acknowledgement of the chord at any time by pressing the FILL IN key (RIFF KEY Fill In mode) or by pressing harder on the keyboard keys (RIFF KEY After mode) just the same as what occurs for the AFTER FILL function."

So, after all this, the only thing the Riff acknowledges is the key you are in, after that, it's whoa nelly! and pray the preprogrammed changes suit you?

Sorry....... Not for me.

Or have I misread this....?