Power maximum output power for each pin
There are also limits on the total power of groups of pins,


  
  The sum of all IOH, for ports J0-J7, G2, A0-A7 should not exceed
  200mA. 
  The sum of all IOH, for ports C0-C7, G0-G1, D0-D7, L0-L7 should not exceed 200mA. 
  The sum of all IOH, for ports G3-G4, B0-B7, H0-H7 should not exceed 200mA. 
  The sum of all IOH, for ports E0-E7, G5 should not exceed 100mA.
  The sum of all IOH, for ports F0-F7, K0-K7 should not exceed 100mA.
  


So you are already limited to 800mA.

Secondly, you have to be careful to change all the pins at exactly the same time. Otherwise some pins will be low, and others high creating effectively a dead short. Or if you make sure the pins are inputs before changing, some pins will be on sooner, and those pins will then for a short period, handle all the current, and thus exceeding their limit for a brief moment. Which isn't that bad, but still not ideal.

So definitely don't use digitalWrite to change all the pins, one after the other.