How do I change the NMI callback for an interrupt in SSP?
You can change the callback for a NMI by editing the file in which it is found and then setting the file to read only so SSP doesn't overwrite the file when it generates code automatically. The NMI file is found in synergy/ssp/src/bsp/mcu/s7g2/bsp_group_irq.c. Note that you replace "s7g2" with the MCU for your target design.
This answer applies to SSP 1.1.x. Check release notes for future releases to see if NMI callbacks are handled differently for that release.