Note that in the 2009 manual, there is a large amount of information on the key process on page 17 including duplication and the fact that you can have up to 8 keys:


"Replacement Keys

NOTE: Only RKE transmitters that are programmed to the vehicle electronics can be used to start and operate the vehicle. Once a transmitter is programmed to a vehicle, it cannot be programmed to any other vehicle.
At the time of purchase, the original owner is provided with a four-digit Personal Identification Number (PIN). Keep the PIN in a secure location. This number is required for authorized dealer replacement of RKE transmitters. Duplication of RKE transmitters may be performed at an authorized dealer or by using the Customer

Key Programming procedure

This procedure consists of programming a blank transmitter to the vehicle electronics. A blank transmitter is one that has never been programmed. NOTE: When having the Sentry Key Immobilizer system serviced, bring all vehicle RKE transmitters with you to the authorized dealer.

Customer Key Programming

If you have two valid RKE transmitters with integrated keys, you can program new transmitters
1. Insert the first valid integrated key into the ignition switch and turn the ignition switch to the ON position for at least three seconds, but no longer than 15 seconds. Turn the ignition switch to the LOCK position and remove the first key.
2. Insert the second valid integrated key and turn the ignition switch to the ON position within 15 seconds. After 10 seconds, a chime will sound and the Vehicle Security Alarm Indicator Light will begin to flash. Turn the ignition switch to the LOCK position and remove the second key.
3. Insert a blank integrated key into the ignition switch and turn the ignition switch to the ON position within 60 seconds. After 10 seconds, a single chime will sound and the Vehicle Security Alarm Indicator Light will stop The new integrated key is programmed. The RKE transmitter will also be programmed during this procedure.
Repeat this procedure to program up to eight keys. If you do not have a programmed RKE transmitter with integrated key, contact your authorized dealer for details.

NOTE: If a programmed key is lost, see your authorized dealer to have all remaining keys erased from the system’s memory. This will prevent the lost key from starting your vehicle. The remaining keys must then be reprogrammed. All vehicle keys must be taken to an authorized dealer at the time of service to be reprogrammed."
I do not believe there are any changes in the 2010 vehicles in this area (no hardware changes) so the process should be the same.