My understanding of BRICKING a unit is to take a functioning unit and turn it into a NONfunctioning unit so screwed up that you can't recover it.
The next step usually involves a trip by said unit to Humminbird Repair.
When you use a SD card to update the unit, make sure that ONLY the new update is on the card. Nothing else.
I'd call HB customer service first thing Monday morning to confirm this. Good luck.
Mike