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You can use https://github.com/timarney/react-app-rewired to override anything in the default CRA config

I don't think this works on CRA 3 and it's development has slowed a lot. craco (listed in the alternatives) supports CRA 3.

I've been using it for a while with CRA 3 / react-scripts 3.2

Works fine for overriding Webpack config at least.