Hows to update material group into contract, Doesn't work with MEMASSCONTRACT nor idoc

Hi,

We need to change material group into Contract. I have read blog that says to use MEMASSCONTRAT transaction however it doesn't work. It give a green light saying that changes on MATKL isn't possible. Is anyone knows how to change the material group. The problem is that material have been re-categorized and they have PO and Contract with these materials, so we need to modify the material group. The client knows they will loose some reporting data, but this is okay with them. The important is that we could use these new material group moving forward.

Thanks in advance.