Don't know if this is possible even, but it would be nice, if the sequencer would make a tie, if I hold the key down whilst pressing rest, so:
Key press = note
Rest press = rest
Key press and hold + rest press = extension og note duration (or noteoff message)
The text file could be" MIDI note nr. for note", "X for rest" and "- for tie"
Just sayin' (wishing)