customkeyDown(int, int, String, String, String) takes note, instrument, volume, effect and effect-parameter and uses them to override playing
notes in the selected channel.
setChanvol(int, int) takes the channel number and the desired channel volume - it will override the channel's mixing volume, possibly with some unexpected
consequences (such as more 'clipped'-sounding volume slides), and may be overridden by some varieties of volume change command in the module's patterndata.
setNext_sequence_index(newpos, behaviour) takes the desired new sequence position and an int 0 or 1 to choose between 'continuous' pattern-skip behaviour
(where the row in the new pattern follows smoothly from the row in the old pattern) and 'play from start' behaviour, where the new pattern plays from row 0.