You can add it:
var meta = document.createElement('meta');
meta.httpEquiv = "X-UA-Compatible";
meta.content = "IE=edge";
document.getElementsByTagName('head')[0].appendChild(meta);
...but I wouldn't be surprised if by the time that ran, the browser had already made its decisions about how to render the page.
The real answer here has to be to output the correct tag from the server in the first place. (Sadly, you can't just not have the tag if you need to support IE. :-| )
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