How do you deal with evolution in the coding standards / style guide in a project for the existing code base? Let's say someone on your team discovered a better way of object instantiation in the programming language. It's not that the old way is bad or buggy, it's just that the new way is less verbose and feels much more elegant. And all team members really like it. Would you change all exisiting code?

Let's say your codebase is about 500.000+ lines of code. Would you still want to change all existing code? Or would you only let new code adhere to the new standard? Basically lose consistency?

How do you deal with an evolution in the coding standards on your project?