Ableton's Recombine transformation generates MIDI clip variations while keeping each note's start position fixed, so the rhythmic skeleton of your pattern stays intact as other parameters shift around it. Pitch, note length, and velocity can all be transformed, or you can lock any of them out using the exclude buttons to control exactly how much changes.
The slider in the graphical interface lets you dial through different transformation states, while Shuffle randomly recombines the note parameters and Mirror reverses their properties across the pattern.