JSFiddle - React, Tailwind, and code Playground

HTML

<p class="transform">ISATV, ISatv, IsATV, ISA, ISAT, ISAV, ISATV, isatv</p>

CSS

.transform { text-transform: uppercase; }

.untransform { text-transform: none; }

JavaScript

var strIsatv = /(ISATV)+/gi;
document.body.innerHTML = document.body.innerHTML.replace(strIsatv, '<span class="untransform">ISAtv</span>');