1. not that I am aware of.
2. native HTC email app does not support push it seems. this may be addressed in a future update. perhaps open a ticket with HTC and advise them you need yahoo push support on their native client. you can install the yahoo app from the store and that will give you push. I know the EVO lte has push
support for yahoo in the htc app.
3. send the dev of the app an email.