JSFiddle - React, Tailwind, and code Playground

JavaScript

var re = /(?!^nin)(nin$)/gm; 
var str = 'suyunin\nabcninshs\nning\ngnin\nning\nkinindan*\nsininteki\nnin\nninkisi';
var subst = 'NG'; 
var result = str.replace(re, subst);
alert(result)