Here's how you mute a pattern track from the song mode.
1) select a track (I usually select an empty track).
2) press menu/edit.
3) press menu/insert.
4) press + 13 times to get to XG Exc Multi.
5) move cursor down once, right twice.
6) press + 4 times to get to RcvCh.
7) cursor right once.
8) press + till you get to the part you want.
Pattern parts are designated from 17 to 24.
9) cursor right once.
10) enter shift-999.
11) press enter key.
12) press exit to quit.
to restore (undo the mute) while in same song.
follow steps but in step ten (10) above, make sure that the Data column matches the Part column in the display.