If in future i need to change the code or some config (which is part of node modules), Is that will be a big headache?
What is the merits and demerits for using create react app?
You can use create-react-app and rest easily knowing that if you need to do any extra configuration at any point, you can always do npm run eject which will make all of the setup create-react-app does for you fully visible. Read more about it here.
I would suggest making a few applications configuring Webpack and Babel by yourself just to understand what's really going on and the purpose of it, but the convenience create-react-app is worth looking in to.
create-react-appwill allow, you can runnpm run ejectto get access to the underlying Webpack configuration. This is a one way operation, however - you can't go back tocreate-react-apponce you've ejected.