Enhancement for VA01 item's pricing date

In VA01, there are 'first date' and 'pricing date' in sales order's item. I want to enhance VA01 to realize: If end user change the 'first date', the 'pricing date' will auto change to the value equal to 'first data'.

For example:

sales order item's first date is 2008/3/25, pricing date is also 2008/3/25.

Then user change the first date to 2008/5/25, I need the pricing date auto change to 2008/5/25.

In that way, sales item's net value will also auto update.

I have try many ways, like bellow:

VA01 EXIT: MV45AFZZ,MV45ATZZ, MV45AOZZ,MV45AIZZ, MV45AFZB

BADI: BADI_SD_SALES

I can't find any enhancement to realize the function.

Could anyone give me some idea?

Cheers! Thanks in advance.

Regards,

Eric .