Is it possible to program the secure boot loader and initial application with JTAG?

I wish to leverage the Secure Boot Loader framework to facilitate OTA updates on the Synergy S7G2. Our product does not require signing or encrypting our application binary or other secure boot functionalities.

Is it possible to program the secure boot loader via JTAG or must it be done using the serial boot mode and factory bootrom?

Is it possible to self-sign the application binaries or put the bootloader in a mode such that it does not authenticate application images?