您可以调度一个新的KeyboardEvent，它以编程方式发送Ctrl+Alt+M。

const sendOffer = () => alert('New email!');

// Original binding Ctrl + Alt + M (cannot modify)
document.addEventListener('keydown', (keyEvent) => {
  if (keyEvent.code === 'KeyM' && keyEvent.altKey && keyEvent.ctrlKey) {
    sendOffer(); // Internal handler logic in application
  }
});

// New binding Ctrl + Alt + X (alias)
document.addEventListener('keydown', (keyEvent) => {
  if (keyEvent.code === 'KeyX' && keyEvent.altKey && keyEvent.ctrlKey) {
    // If Ctrl + Alt + X it pressed, send Ctrl + Alt + M
    document.dispatchEvent(new KeyboardEvent('keydown', {
      code: 'KeyM',
      altKey: true,
      ctrlKey: true
    }));
  }
  keyEvent.preventDefault();
});

<button
    onclick="sendOffer()"
    title="Send offer by e-mail [Ctrl+Alt+m]">
  Open in new tab
</button>

上面例子的后半部分可以放入用户脚本（Violentmonkey、Greasemonkey等），并在需要密钥的网页上执行。

// ==UserScript==
// @name        Custom keybindings for company website
// @namespace   Violentmonkey Scripts
// @match       https://my-company-website.com/*
// @grant       none
// @version     1.0
// ==/UserScript==
(() => {
  // New binding Ctrl + Alt + X (alias)
  document.addEventListener('keydown', (keyEvent) => {
    if (keyEvent.code === 'KeyX' && keyEvent.altKey && keyEvent.ctrlKey) {
      // If Ctrl + Alt + X it pressed, send Ctrl + Alt + M
      document.dispatchEvent(new KeyboardEvent('keydown', {
        code: 'KeyM',
        altKey: true,
        ctrlKey: true
      }));
    }
    keyEvent.preventDefault();
  });
})();

注：following website有助于诊断键盘事件。

如果您仍然感到困惑，请参阅documentation on MDN。