Adding to module.exports on cypress/plugins/index.js file Cypress

Solution 1:

I believe that you can pass in the config from your function to your require and then return that new config.

module.exports = (on, config) => {
  // `on` is used to hook into various events Cypress emits
  // `config` is the resolved Cypress config
  const file = config.env.configFile || 'qa';
  let newConfig = getConfigurationByFile(file);
  
  require('cypress-grep/src/plugin')(newConfig);
  
  return newConfig;
};

Since your getConfigurationByFile() function returns a JSON Object like the original config, and the cypress-grep plugin takes in a JSON Object, you can probably just add the resolved JSON from getConfigurationByFile instead of the standard one provided by config.