Sure, but the macro function is a normal function - it has inputs, outputs, and (preferably) should be pure. There's nothing special about the macro function itself, really.

You can see it explicitly in Common Lisp, where you can easily access and replace a macro-function with a custom one that you DEFUN yourself, like this.

    CL-USER> (defun my-quote-fn (form env)
               (declare (ignore env))
               (destructuring-bind (operator &rest body) form
                 (assert (eq operator 'my-quote))
                 (list* 'quote body)))
    MY-QUOTE-FN

It's a perfectly normal function, I can call it right away:

    CL-USER> (my-quote-fn '(my-quote (+ 2 2)) nil)
    '(+ 2 2)

I can also tell the compiler that this perfectly normal function is a macro function...

    CL-USER> (setf (macro-function 'my-quote) #'my-quote-fn)
    #<FUNCTION MY-QUOTE-FN>

...and the compiler will start using it to expand macros:

    CL-USER> (macroexpand-1 '(my-quote (+ 2 2)))
    '(+ 2 2)
    T

What is special about macros, and what you describe as the "feature that cannot be implemented", is the language's ability to call that function at compilation time and feed its output back into the compiler. This is the link that is missing in most programming languages.