Adding a new mapping does not delete any of the existing ones. If you want to 'move' a product from one entity to another, it'll take both an add, and a delete. If multiple mappings are being removed, you may want to use the ClearMappings node.
At least one of EntityID or EntityGUID and ProductID or ProductGUID must be provided.
Since there is no 'update' action, changing a product's display order within an entity with this node would require both a delete action (for the old display order) and an add action (to set the new one).
Warnings:
None
Example(s):
Add a mapping from Product 14 to Category 3.
<Mapping Action="Add" EntityType="Category" EntityID="3" ObjectType="Product" ObjectID="14" DisplayOrder="4"/>