This rule completely overwrites the original values of the element. One of the most commonly used rules.
You have a selection of goods that represents all products whose MANUFACTURER element contains the term Bosch Technologies, but you know the correct name is Bosch. So you create an Overwrite rule, insert the correct value, and apply this rule to the saved selection of Bosch Technologies. You also set the target element for the MANUFACTURER and insert the Bosch text as the new value.
Similarly, you can use the rule if you need to replace the contents of one element with another - like PRODUCT for PRODUCTNAME. You create a rule to select all products that overwrite the values of the original PRODUCT to PRODUCTNAME (use the % tag to assign the element, the system will automatically offer the elements to you).