In SynthEdit pitch is represented in Octaves. For example to lower a pitch signal 1 Octave, subtract 1.0 from it (using a subtract module).
To lower a pitch 1 semitone, subtract 1/12 from the pitch signal. (there are 12 semitones in 1 octave).
To lower the pitch 1 cent, subtract 1/1200, because there are 100 cents in one semitone (and 12 semitones in 1 octave).
For your example, -31 cents, subtract 31/1200 ( which is 0.02583333 ).