Can my board handle an additional of 0.1 mA if it is already have a current of 0.1 mA

Like extra current put in?

Hi, databoy.
Don't you mean 0.1A (100mA), not 0.1mA? The rating of 0.1A is how much current your circuit will draw. If you have a wall adapter that can source 5V 1A, then your board will only draw 0.1A, meaning no damage will be done. It is important to isolate your power supply, though, from the USB port.
Der Strom