Under what circumstances can you change the material type for a material if stocks, reservations,...

In SAP S/4HANA, changing the material type (transaction MMAM) is restricted if stocks, reservations, or purchasing documents exist, but it’s allowed under specific conditions:

The quantity and value updates are the same(A): The old and new material types must have identical quantity and value update settings in their valuation areas (configured in OMS2, Material Type Customizing). For example, both must update quantity and value (e.g., "FERT" to "HALB"), or neither (e.g., "NLAG" to "DIEN"). If these differ, the change is blocked due to inconsistencies in stock valuation.

The same base unit of measure is used(C): The base unit (material master, Basic Data 1 view) must remain unchanged between material types. Changing it (e.g., from "PC" to "KG") would invalidate existing stock or document quantities, so the system requires consistency to allow the type change.

The same batch management level(B) (e.g., plant or material level, configured in OMCT) is not a strict requirement—batch settings can differ as long as other conditions are met.The same account category(D) (e.g., General Ledger account determination) influences posting but isn’t a prerequisite—account assignment can be adjusted post-change. This is per SAP’s material type change rules.