Just a thought, which may or may not be helpful...
On my PSR-E models I've had to figure some things out by recording specific actions in a User Song, then looking at the MIDI events that were recorded in the User Song to see which events were being used to do certain things.
If using the pedal to control the DecayStrings is something that can be recorded in a song, you might try making a short recording where you play a few keys with the voice in question and then use the pedal to trigger the decay effect right away. Then you can try to export the recording to a MIDI editor so you can inspect the events in it.
On my PSR-E models, many of the things I was interested in could not be exported in a normal MIDI file, so I had to save the entire memory as a Backup File, then search for the User Song within the memory backup. It turned out that the actions I was interested in were being done with Sequencer-Specific Meta Events, which are a special type of System event that are specific to a particular device (sequencer, keyboard, etc.) or family of devices (such as a given line of models). Meta Events can only be used in MIDI files; they cannot be transmitted within a stream of live MIDI events, because the Status Byte for a Meta Event in a MIDI file is the same as the Status Byte for a System Reset event in a MIDI stream! And since the particular Meta Events that were being used were Sequencer-Specific, they would only work on Yamaha models that are designed to respond to them as intended, hence they couldn't be exported from an internal User Song to an external MIDI file that wouldn't be able to work as intended on some other make and model of keyboard.
Anyway, if your RD2000 has an onboard song sequencer that lets you record, you might see if the pedal can be recorded, and whether the DecayStrings responds properly when the recording is played back. If it does, then you can see whether the recording can be exported to an external MIDI file.
Or you might even try something simpler-- connect to a computer and monitor the MIDI as you play, and see if the pedal produces MIDI events, and if so, which ones.