A code can be inherited/included/copied and then customized manually from the programmer. This a form offeature/syntax-abstractions. When the origin code is modified, the programmer is informed if he want to customize again also the destination code.
OOP ideally follows the Lisokv Substitution Principle, but sometime there are exceptions to contracts. So code patching can increase code-reuse, because one can reuse piece of code and patch it, without creating a complex OOP structure.