Raspberry and Xbee Series 2

Hi all, i am creating a sensor network using Raspberry and Xbee series2 (xb24-z7wit-004) using python language because it offers a library to program this device.
For different reasons i dont want use Link Key, but i want encrypt my data.
My ideas is that: enable encryption on the Coordinator network with Link key and Network key, but in my node, i want disable encryption in XBee but encrypt my data using python program.

I have 2 questions:

1- If i set the Xbee like AT mode, it is possible to set KY( network key) using a AT command and encrypt my data using Xbee?
2- If i set the Xbee like API mode, it is possible to create a payload encrypt( with AES 128 bit) and send that to a coordinator? Theorically the coordinator can read this data

Yes you can set the KY using AT commands but unless you use the encryption EE1, it is not going to encrypt the data.

What you most likely want to do is to encrypt the data within your application before it is added to the API frame or sent to the radio using transparent mode. This keeps you from using the radios encryption functions which then are used for association as well but allows you to encrypt/De-crypt the data.