我已经在< 使用不同的用户代理加载iframe内容>

I already answer the same question at <Load iframe content with different user agent>

为方便起见，我复制并粘贴了答案：

For your convenient, I copied and paste the answer here:

首先，您必须创建一个函数来更改用户代理string：

First of all, you must create a function to change the user agent string:

function setUserAgent(window, userAgent) {
    if (window.navigator.userAgent != userAgent) {
        var userAgentProp = { get: function () { return userAgent; } };
        try {
            Object.defineProperty(window.navigator, 'userAgent', userAgentProp);
        } catch (e) {
            window.navigator = Object.create(navigator, {
                userAgent: userAgentProp
            });
        }
    }
}

然后你需要定位iframe元素：

Then you need to target the iframe element:

setUserAgent(document.querySelector('iframe').contentWindow, 'MANnDAaR Fake Agent');

您还可以为iframe设置ID并定位ID而不是页面上的所有iframe元素。

You may also set an ID to the iframe and target the ID instead of all iframe elements on the page.