Thank you for your message.
I have dealth with an attempt to change page title in transformation so I can confirm that this is not possible. The page state in which the transformations are resolving is after the last chance you have for changing page title.
You can change the page title programatically outside the transformation, although its better to use our settings for that in page properties. You can also use macros there so you might create a custom macro to get your page title.