Webpack describes HMR on their official site as bypassing browser reloads entirely: you hit save, the page hotswaps the webpack chunks, now your webpage has the updated code ready to go, like "changing styles directly in the browser's dev tools." It also mentions this is something the "application" has to manage, which I assume is Experience Builder in this context, so we'd need someone with tons of internal ExB knowledge to weigh in on if this is feasible or not.