Importing MIDI one voice per stave

Basically I'm using a MIDI file that was originally exported from MuseScore into an ABC notation programme (where the voices 1-2-3-4 were automatically sorted into one voice, and notes tied as appropriate), and has been exported again from that software and imported back into MuseScore. MuseScore automatically reassigns the voices in each stave where I would prefer to keep them as one voice per stave for various reasons - as chords with notes tied instead of separate voices. Is this something that can be reverted in MuseScore or does the MIDI file itself have to be manipulated in some way? or is this not possible

I know there's the option of using MusicXML, but for some reason when exporting to this filetype from the ABC programme, some accidentals are missed out when imported back into MuseScore (but I think this is to do with the MusicXML file itself).