Can MRP take into account material determination?

We are looking at using material determination to help phase out an old material and replace it with a new material number.

I.e. we need to change a material number. The new material and old material are pretty much identical. (basically changing some mtrl numbers to match a new mtrl numbering standard). It looks like we can use material determination in SD to ship out the old material number until the old material stock is gone.

Our question is however to figure out how to set up MRP. How would we set up MRP to "see" the old material number as available stock? We have significant stocks in some cases of the old material number and we don't want to trigger production of the new material number. (planning should be done under the new material number)

Any ideas?

Thanks!

Craig