Download the Data List from Yamaha, it tells you a lot. For kit 040 RealTimpani, it looks like the mute switch is turned on for all internal pads except 3, which has a start and stop roll. If the MIDI notes are to be believed as a representation of pitch, it looks like this:
G# | A | A#
F# | F | G
D | D# | E
B | C | C#
It might not actually be that way though. You can change these notes by getting into the Voice Tuning page (VCE2-1). For all pads except 3, it's as simple as selecting the desired note. For pad 3, you have to know how many half-steps to add or subtract. For example, if you want to make the Bb roll on pad 3 a C roll, you need to add 2. Don't forget that you have to modify two notes (layers A and C) for each pad except 3.