Nope, it doesn’t. When you copy a variable into another variable, behind the scenes PHP will only make that variable refer to the same data, so it only uses a little more. When you start manipulating the data (so $_GET and $get diverge), PHP will create a copy.
So if you just like to do things your way without manipulating $get, you can do so. If you want to be absolutely sure, you can do
$get =& $_GET; // Hmm… Or perhaps it was &=
which means that $get references $_GET, and thus that they refer to the exact same data. So when you manipulate one, the other is also altered.
Yet, I’d recommend you to follow standard PHP practice (i.e. use $_GET instead of $get) because you might get in trouble if you ever have to work with other developers.