dronf.js

var x = require("./fnord");

module.exports = function foo() {
    console.log(x(1, 2));
};

fnord.js

module.exports = function (a, b) {
    return a + b;
};

foo.js

var x = require("./fnord"),
    y = require.resolve("./fnord"),
    z = require.cache[y].exports;

require.cache[y].exports = function (a, b) {
    console.log("got", a, b);

    return z(a, b);
};

var t = require("./dronf");

t();