Does installing this certificate mean I irrevocably trust HueStones?
No. Installing this certificate simply allows your browser (or email client) to automatically confirm that signed software (or email) from HueStones has not been tampered with and is genuine. Your browser or email client will usually display a message confirming this. It is up to you to choose to install the software or read the email given the additional knowledge that it is genuine and vetted by HueStones. If at this time you choose not to trust HueStones, you can cancel the installation or delete the email.