If you're asking about the instrumental soundpool objects (loops), they are what they are, so you can't change a major to a minor for example.  In later versions of MMM, there are numbered bars above the media pool that allow you to choose alternate keys or versions of a soundpool object.  If those don't give you what you need, you can transpose by timestretching any object to your liking.

However, in the Vita MIDI Editor you can play, or ""write" using the instruments in any key or scale you wish.