need to lower guitar pitch by a scale octave for midi output

[Patrick Stanistreet]

I wrote in an earlier note that I am converting my 1.6.10 lily files
to 2.2.0 and for the most part it is working.  The code that I was
using to lower the midi pitch of the guitar an octave does not
seem to be working,
Here is the convert-ly output

    \set Staff.midiInstrument = #"acoustic guitar (nylon)"
    \set Staff.instrument = "guitar"
    \set Staff.transposing = -12

Lily doesnt like the above code though, so I would like to know how
to get the  pitch lowered.   
Thanks