Tools like xsd or T4 (in the .NET ecosystem) are great time-savers, but you would never consider directly modifying the code they generate. You would leave the generated code untouched (in case it ever needed to be generated again) and subclass it to make whatever changes you intend.

I think Copilot is so unfortunate because it's not building abstractions and expecting you to override parts of them. It's acting as an army of monkeys banging out Shakespeare on a typewriter. And the code it generates is going to require an army to maintain.