How to change a plant in sales order for main item of BOM

Dear Gorus,

Please tell me how we can change plant of main item of a BOM?

Actually, I have maintained a LUMF BOM. The main item and components of this are maintained for two different plants. BOM is also maintained for both the plants and it explodes smoothly in sales order once I provide the plant. But as per our reqirement sometime we need to change the plant. Here system does not allow to change the plant of main item of BOM as it is in gray mode now.

Please guide me how can I change the plant? Is it possible by configuration or should I go for userexit?

If the userexit required please tell me which userexit I have to use because I already discussed and checked with my ABAPer. we could not find the right userexit.

Thnaks in advance.

regards,

Sanjay