If you are looking at using the buyer group in AX for helping with managing different groups of planners. You might want to evaluate the defaulting that happens onto the planned order from master planning. You can assign a buyer group to a vendor and to the item. So you might want to review the defaulting logic of which buyer group gets put onto the planned order. What will happen is that if you have a default vendor associated with the item then the buyer group on the planned order will come from the vendor. If you don’t have a default vendor on the item the buyer group will come from the item.
AX2012 R3 CU11
One thing to keep in mind, before you can firm the planned purchase order you will need to assign a vendor, when you assign the vendor the buyer group will be changed to the group on the vendor.