JSFiddle - React, Tailwind, and code Playground

JavaScript

var myString = "This is the original string. Let's see if the original will change...";
var myRegex = new RegExp('original', 'g');
var matched=false;

document.write(myString+'<br>');

myString = myString.replace(myRegex, function (match) {
    
    if ( !matched ) {

        matched = true;
        return 'replaced';

    } else {
        return match;
    }
});

document.write(myString);