Automatic Adjustment for retro billing for debit memo.

Dear FI Experts,

We have little bit confusion on Retro process debit memo how this to be posted.

Ex: Normal invoice created with the value of 1000 rs for certain period of time.( JAN1st till March 3 )

Now business change the price during that period ( JAN1st till March 3 ) to 1050 rs

Now SD consultant complted debit memo process by using retro active.

Here in the debit memo billing,Value is 1050 rs.

How we can adjust 50 rs amount from FI point of view, this should be possible automatically in Transaction code F-28 ?

Please suggest.

Regards

Pulak