Not sure I understand. Do you mean multiple semi-finished products for the same parent that have different BOM codes? I know that the storage site and requirement parameter BOM code are a one to one match. Sage wanted to do something with the planning site vs production site on work orders but that never came to fruition. Would be a boon for us if one could call out the planning site parameters regardless of the BOM code. Maybe some day...

Hi John,

Thanks for your advise. We've some semi-finish product which has multiple BOMs and each BOM is assigned to a different BOM code and since Requirements parameter setup is one to one( 1 Storage Site to 1 BOM Code), how can we do the setup for multiple BOM code using the same Storage Site. 

Please see the below screenshot.

In that case, you would want different BOM codes for the parent as well. They can all produce the same product, just using different BOM codes to do it. MRP will then look down the chain ParentBOM3 suggests ChildBOM3, ParentBOM2 suggests ChildBOM2, all produce product XYZ.

The Semi-finished product has certainly 1 BoM alternate that is frequenlty used or cheapest. Use this BoM with the BoM code matching the MRP setting. My recommendation would be to set this SF product-site record with a reorder policy with no pegging. As a consequence the MRP won't see the demand on the components until the SF work order is created. 
1- You run the MRP for the first time
2- You create / modify WO on all finished products (using the selection formula in the Enterprise planning function)
3- You create / modify WO on the semi-finished products paying attention in selecting the suitable BOM code
4- You run the MRP for the second time -> now the pegging demand on the SF components is consodered in the MRP suggestions
5- You replenished the stock of the restof the products

I hope it makes sense to you.