Hi,
If you are inserting planned delivery cost conditions in PO and you are posting different priice in MIRO-planned delivery cost, the inventory will be adjusted accordingly. You can test the scenario and confirm.
Alternatively, if you want to use unplanned delivery cost you can define whether the unplanned delivery cost is to be loaded in seperate GL or to be distributed in the GL.
Please check the following threads for more details.
http://scn.sap.com/thread/1137891
http://scn.sap.com/thread/3367368
Hope its helpful.
Regards,
AKPT