You can't add another Unique power - they'd both fire the same script, so there's no point. You CAN add a spell as well as a unique power, and modify the spell script to do something different. Or, you can simply have the crystal initiate a dialogue and give the player options for both north and south pole in that dialogue. Or, you can combine approaches, having a spell do the teleport (You'd have to edit the spell script, checking for GetSpellCastItem(), and comparing resrefs to make sure it's the crystal casting), while the unique power toggles between the two destinations, either by means of the unique power script setting a var on the crystal that is checked in the edited spell, or by means of setting such a variable in a conversation. If you're looking for simplicity, I would just have the item start a convo, and do everything from there.
Funky