All the commands in musescore according to musescore:
From cmd.cpp:
note-c note-d note-e note-f note-g note-a note-b 
chord-c chord-d chord-e chord-f chord-g chord-a chord-b
insert-c insert-d insert-e insert-f insert-g insert-a insert-b
fret-0 fret-1 fret-2 fret-3 fret-4 fret-5 fret-6 fret-7 fret-8 fret-9 fret-10 fret-11 fret-12 fret-13 fret-14
toggle-visible
reset-stretch
mirror-note
double-duration half-duration
inc-duration-dotted
dec-duration-dotted
add-staccato add-tenuto add-marcato add-sforzato add-trill
add-up-bow add-down-bow
add-8va add-8vb
note-longa note-longa-TAB
note-breve note-breve-TAB
pad-note-1 pad-note-1-TAB
pad-note-2 pad-note-2-TAB
pad-note-4 pad-note-4-TAB
pad-note-8 pad-note-8-TAB
pad-note-16 pad-note-16-TAB
pad-note-32 pad-note-32-TAB
pad-note-64 pad-note-64-TAB
pad-note-128 pad-note-128-TAB
reset-style reset-beammode reset-groupings
clef-violin clef-bass
voice-x12 voice-x13 voice-x14 voice-x23 voice-x24 voice-x34
pad-rest
pad-dot pad-dotdot pad-dot3 pad-dot4
beam-start beam-mid no-beam beam-32
sharp2 sharp nat flat flat2
flip
stretch+ stretch-
pitch-spell
select-all select-section
add-brackets
acciaccatura appoggiatura
grace4 grace16 grace32 grace8after grace16after grace32after
explode implode
slash-fill slash-rhythm
resequence-rehearsal-marks
del-empty-measures
add-audio
transpose-up transpose-down
delete
full-measure-rest
toggle-insert-mode
pitch-up pitch-down
time-delete pitch-up-octave pitch-down-octave
pad-note-increase pad-note-decrease pad-note-increase-TAB pad-note-decrease-TAB
toggle-mmrest toggle-hide-empty
set-visible unset-visible
system-break page-break section-break
relayout

From scoreview.cpp
escape
note-input
copy cut paste paste-half paste-double paste-special
swap
lyrics
figured-bass
mag
play
fotomode
add-slur add-hairpin add-hairpin-reverse add-noteline
chord-text title-text subtitle-text composer-text poet-text part-text system-text staff-text expression-text rehearsalmark-text instrument-change-text fingering-text
edit-element
select-similar select-similar-staff select-dialog
page-prev page-next page-top page-end
select-next-chord select-prev-chord select-next-measure select-prev-measure select-begin-line select-end-line select-begin-score select-end-score select-staff-above select-staff-below
next-chord prev-chord next-track prev-track next-measure prev-measure
pitch-up-diatonic pitch-down-diatonic
move-up move-down
up-chord down-chord top-chord bottom-chord
next-segment-element prev-segment-element
next-element prev-element
first-element last-element
rest rest-TAB
rest-1 rest-2 rest-4 rest-8
intervalX
tie chord-tie
duplet triplet quadruplet quintuplet sextuplet septuplet octuplet nonuplet tuplet-dialog
repeat-sel
voice-1 voice-2 voice-3 voice-4
enh-both enh-current
revision
append-measure insert-measure
insert-hbox insert-vbox append-hbox append-vbox
insert-textframe append-textframe insert-fretframe
move-left move-right
reset
show-omr
split-measure join-measures
next-lyric prev-lyric
add-remove-breaks
copy-lyrics-to-clipboard
realtime-advance
advance-longa
advance-breve
advance-1 advance-2 advance-4 advance-8 advance-16 advance-32 advance-64
prev-measure-TEXT next-measure-TEXT
prev-beat-TEXT next-beat-TEXT
string-above string-below
text-word-left text-word-right
concert-pitch