Can I add or remove materials from a Manufacture?
Yes, materials can be removed from or added to a manufacture.
On your Add Manufacture form, the current recipe for the Product / Variation will be populated into the form by default. From here, you can remove ingredients not used for this particular manufacture or add new materials (good for the case in which minor customisations are made without requiring a new variation).
Changing the Recipe for a Product / Variation will not change the materials in any Manufactures already saved - the changes will only apply for all new manufactures added after this point. This is to ensure that in the case where you improve a recipe and change several materials, all past manufactures that used the "old" recipe will be preserved with their true costs.