gatsby-plugin-replace-path

$ yarn add --dev gatsby-plugin-replace-path

$ npm install --save-dev gatsby-plugin-replace-path

// gatsby-config.js

module.exports = {
  // ...
  plugins: [
    {
      resolve: 'gatsby-plugin-replace-path',
      options: {
        pattern: /(e)/g,
        replacement: ( _, match ) => match.toUpperCase(),
      },
    },
  ]
}