Erm... not really.
You CAN create a new function called DrawImage(), for instance, but each time you use DrawImage (the Blitz command) after that, it will call your function instead.
Further more, if you did create your own function called DrawImage(), then tried to use Blitz DrawImage within that function, Blitz will freeze up for a few seconds before causing a stack overflow due to your function repeatedly calling itself.
You CAN create a new function called DrawImage(), for instance, but each time you use DrawImage (the Blitz command) after that, it will call your function instead.
Further more, if you did create your own function called DrawImage(), then tried to use Blitz DrawImage within that function, Blitz will freeze up for a few seconds before causing a stack overflow due to your function repeatedly calling itself.