Wow, I feel like I should've jumped in much sooner...
Bogdan is 100% correct. You don't use the same exact distance between notes in semitones due to the nature of scales (+2,+2,+1,+2 +2+2,+1, etc) not having the same number of semitones between *intervals* (which Kurt also correctly pointed out).
When you Harmonize in C scale, even if you use a drop 6th harmony (requires the least amount of variation to maintain), at some points the harmony will be 8 semitones below the melody (C/E), at some points 9 semitones (B/D) and that's just music theory... Intervals are not the same as fixed semitone rangers *unless* you want to play in a 6 note, atonal scale? Which I doubt!
No, there wasn't an *additional* way to do this on T5 per se; but it *can* be accomplished on any Yamaha arranger. The simplest method I can think of is to assign pitch bend to a foot pedal, then specifiy the pitch bend up range (in the case of the OP's desired effect, +6 semitones) and then depress the pedal when needed.
And since you can assign pitch bend to 0 for the other 2 right voices, this is a simple way to produce the intended effect. There are other ways, including reassigning a mod wheel to do the pitch bend, and just leaving it shoved to the top (but as the Genos no longer has a mod wheel, maybe that's what you were thinking of). However, if you hit "lock" with the joystick all the way up, after assigning the Y axis to pitch bend, you'll get the same result.
And yes, you could use a pitch change DSP, but the effect won't be quite the same, as the notes, as you're shifting the sample at that point (try it, it soudns terrible). Actually, pitch bending the note is also shifting the sample (but in a midi triggered way, so it's better). Best of all would be if they allowed us to program a midi harmony with 0 source and 100 for the midi transposed notes (which you also have to do for the pitch shift dsp)
Mark