Rikki's right. If you don't know, don't touch!

You can find a midi spec here http://www.midi.org/about-midi/specshome.shtml which explains the codes.

The ones I find useful are Expression and the filter adjustment ones, and I occasionally mess with attack and release time.

Expression is a "relative volume" control. I use it to adjust the volume of a track in a midi file without embedding volume change message. If you emberd volume change messages it becomes very tedious when remixing a file if you want to take a track up or down throughout, bcause you have to edit all embedded track volume messages.

Also MSB means "Most Significant Byte" and LSB means "Least Siginificant Byte". I'm not sure the 2k responds to this anyway, I find most parameter changes I use on Yamaha kit involves System Exclusive and at this point you are in bother because I don't think the on-board sequencer lets you edit SysEx.

Have a play with a PC sequencer such as Sonar; its a darn sight easier IMHO.