Well to save Mr. Muskrat some time, I will post the method he gave me to reconstruct a midi file from a mididump.txt.

#put a "use MIDI;" at the top of the dump
#and assign a variable $opus
use MIDI; 
$opus=MIDI::Opus->new({ 
  'format' => 1,
  'ticks'  => 96,
  'tracks' => [   # 3 tracks...
......
......
......
#then as the last line
$opus->write_to_file('mynew.mid');
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