Allow late stage stamp metadata editing

[koresar]

This fixes an unexpected behavior of late stage stamp editing.

This code executes initializers:

const stamp = compose(Something)
  .compose({ initializers: [function () {
    console.log("I don't want this line executed");
  }]});

delete stamp.compose.initializers; // Don't want!!!

stamp(); // will log to the console

After the PR the initializers will not be executed as expected.