Most sequencer programmes for Midi will accept a MIDI Data Dump.
That dump will also contain the Syst.Ex messages.
I don't know about a Syst.Ex message editor.
Normally before any Midi File starts playing it will first send out the Sys.Ex. messages, so you can always find them in the beginning of any Midi file in the editor of that programme.
Usually the Syst.Ex message contains the information about the MIDI Tool you are using. It may be your keyboard, soundcard, Rythem box, or Midi guitar.
This way the Midi-file to play knows if you use YAMAHA(XS)or Roland(GS)files or whatever equipment you are handling.
[This message has been edited by Hano (edited 06-21-2000).]