Yeah, that command should work.

Try

[ir_translate]
000002.LM=Shuffle ; if in the Mp3 player, a long press of the right button = shuffle

failing that....

[ir_translate]
000002.LM=20DF0D ; if in the Mp3 player, a long press of the right button = 0 on rio remote

oh, and make sure you don't have any other translations for the right button before the Long one.