Google Feed Extension - help needed

Hi,

For google feed i am using the standard google feed extension that comes with OpenCart.
As per recent google merchant center changes and some other issues i have, i need to update following fields:

1. Identifies Exist Value FALSE - i want to set it for my products
2. Shipping information - i updated shipping free in google but it says shipping details missing
3. Google Product category

What all changes needs to be done in system configuration or in code for it
Or any extension which help me in all this and support auto-submit to google as schedule

Thanks