Morphs are linear combinations, so if you give your 'modified face with puckered lips' morph a weight 1.0 and your 'modified face' morph a weight -1.0, the result will be a morph with just the puckered lip change.

The transfer may have triggered some other minute changes, resulting in residual deltas not large enough to give a visual effect but large enough to let Poser conclude there is a difference. Set of deltas may be larger than necessary.