The supplied soundpool samples are what they are. You can't make a minor out of a major, and you can't change the order. That is unless you are a programmer and can hack the software.
However, you CAN pitch-shift any sample up or down a half step (or more) using the pitchshift feature.
Beyond that, your only option is to create your own chord sequences in the Vita MIDI editor either by drawing them in, "playing" your computer keyboard, or using an extenal MIDI controller keyboard.