Substituion of profit center while posting to internal orders

Question

Dear experts
Can anyone guide me to substitute a different profit center while posting to a real internal order.
I tried substitution rules, user exits, etc.  Eventhough the control goes there, substituion is ineffective since profit center assigned to the internal order in its master data is getting replaced again.
Any other work around is possible to achieve this.
Thanks

Answer 1

Find below your clarification for the points
Why we assign cost center while posting to any G/L, even though we have been assign cost center to the cost element it will post the co entry through cost element.: Once you have assigned cost center to cost element in T.code OKB9 or KA01, no need of manually entering the cost center for the respecting primary cost GL while passing enteris.
Please any one make me understand the internal logic and process of how cost element and cost center works.: Whenever you post a cost to primary cost element , you require an object in Controlling , such as cost center to identify the costs. This primary costs are only created when the respective GL exist in the operational chart. Cost center is the location where cost incurs. Thus when you assign the cost to cost center , the cost will be booked against that particular location .