A/P Invoice due date user can't change

Hi Export,

When we making A/P Invoice due date coming automatic based on supplier payment term setup.

We required...

1) When we post A/P Invoice if user change due date than A/P Invoice goes for approval.

2) After adding the A/P Invoice if user update due date than system block through transaction notification.

Please suggest how to validate.

Thanks in advance

Mukesh Singh