An addendum to Lalversons comments.
To make posing the prop easier you could try this, Ill assume the prop is parented to the right hand, and you want to change it to the left hand:

1. Load a character, set all its body and hip rotations and translations to zero (using Restore Figure from the Edit menu will usually do this, but not always, so check).
2. Make sure the pose is left right symmetrical (use symmetry functions from Figure menu if necessary).
3. Load the smart prop, change its parent to the UNIVERSE.
4. Take down a note of all rotation values for the prop, and the value for its x translation.
5. Now translate the prop to the left hand. You can just enter the value by clicking on the dial, if the value you noted down was 0.332, then the new value will be 0.332
6. The same applies to the rotations, any that you need to change will be the inverse of the ones you noted down (you should only need to change two at most, probably Y and Z).
7. Finally when you have set all the rotations, set the parent to Left Hand, and resave the prop.