I need to accompany a song in a lower key because the published version sits too high for my voice. The product page offers a PDF and sometimes a MIDI file, but I cannot see a key selector. Is it practical to transpose the purchased material myself, and will the chord symbols and piano voicing remain usable after doing so? I am especially interested in whether MIDI makes this easier or whether the shop can prepare another key on request. What information should I provide so that the vocal range, accompaniment, and playing difficulty are adjusted musically rather than shifted mechanically?