Editing XBee Series 1 module's firmware

I am new to XBee. I want to implement a different encryption in the communication between two XBee 802.15.4 Series 1 modules. I have used XCTU and saw the encryption is AES 128 but I want to use something else.

  1. Will I be able to edit/reprogram the coding used for XBee 802.15.4 Series 1 to change encryption?
  2. If yes, please let me know the procedure.
  3. If No, please let me know with which module I will be able to accomplish this job.

Thank you in advanced for your response. It’s really very urgent for me.

Not as far as I am aware. Though you could use a Programmable xbee or external device to handle the custom encryption depending on your requirements. (?)

AES 128 bit encryption is the standard encryption. Is there any specific reason to use different encryption?