Previewing your menu before launch
If your site is already live, then you likely will want to preview your new mega menu before you launch to all customers.
Our first recommendation would be to have a test environment where you can test large-scale changes like a site navigation change in advance.
All of our apps are free on sandbox environments so there's no additional cost for this.
Add to a test page
We understand that having a sandbox environment isn't always possible. In that situation, we would suggest using a non-global region. The typical installation process involves adding the menu to a global region in the header but, being global, this affects every page. If you were to add to a non-global region you might be able to test a localised version of the menu. E.g. a region on a regular web page.
Make live but be ready to roll-back
Failing that, we would offer the suggestion to prepare your menu and make it live during a quiet period. If you spot an issue, you can remove the page builder widget, publish, and your original menu will be back. If you would like, you are always welcome to reach out with support to discuss.