Yes you can still backup your nand , almost all bricks are repairable , some with a softmod some with reflashing the nand , but it is fair to say that if your read the guide modmii generates for you and follow it to the letter then youll be safe , its only deviating from the guide and messing with things you dont understand will cause you a brick . You will have priiloader also , which allows you another level of protection.