How to transfer inventory from multiple items to one NEW item

We have a project to reduce our raw materials list. Currently, one generic raw material have different item codes, each being dependant of the supplier.

Our plan is to :

- create ONE generic item code for one physical raw material

- transfer the inventory from the non-generic item codes to the generic item code

We need the inventory value of the generic item code being calculated based on the sum of the non-generic ones (globally speaking, at plant level the inventory value must not be changed).

How to proceed in terms of steps to go through in JDE, in order to achieve those transfers with the right costs ?