What Is the Difference between a State Change and a Code Change in a Deployed Smart Contract?

A code change involves altering the fundamental logic or functions of the smart contract, which is generally impossible due to blockchain immutability. A state change, however, involves modifying the contract's stored variables, such as account balances or ownership status.

State changes are the intended and common result of a contract's execution, while code changes require specific, often controversial, upgrade mechanisms.