i use a single preset for everything.
if i needed to implement tempos per song for a gig tonight, i would duplicate the preset for each song, change the preset name to each song, and store the tempo.
same preset, just tempo changed (at first), and preset title confirmation for the song.
and from there, if i want or need to make changes to things for each song, i can since they're all separate presets now. add a flanger to one and not the others, etc.
i think preset per song is the best way to adjust for songs that absolutely need different things no matter what it is.