There's no simple answer to this question, as it can depend on several factors. An addendum is essentially an amendment to a contract, so it can be used to change specific provisions in the contract. However, an addendum can also add new conditions to the contract. So, whether or not an addendum overrides a contract depends on what the addendum says and how it affects the rest of the contract.
If you're trying to figure out whether an addendum overrides a contract, you'll need to look at the language used in both the original contract and the addendum. Based on that language, you'll need to determine whether the intent of the addendum