[X] Defiance. Established doctrine is wrong, and the words of the Ecclesiarchy a betrayal of the God they claim to revere. Such a clean break makes further changes a lot easier to introduce, but makes you much more vulnerable to accusations of heresy and invites direct opposition.
[X] Philosophy. Construct a system of quotes, teachings and doctrine from across the ages that can be used to justify your new approach. Such a change of belief will be wide-reaching and thorough, but requires more time to convey and is easier for other priests to engage with and attack.
[X] Revelation. Present your new philosophy as a direct command from the Emperor himself. This is the easiest explanation for the average citizen to accept, but it is also self-contained; any change will be focused and limited to the precise topics of the 'vision', for better or worse.