Sublime Text 3 works for me.
But you should make sure that Regex is really the tool you need.
You didn't say just what you are changing.
If you are e.g. changing CSS classes or IDs, or Javascript variable names, you should consider refactoring tools rather than regex. Most IDEs and editors that accept plugins have a number of alternative refactoring tools available. Such tools parse and "understand" your HTML, CSS, JS and can make it easier to perform these tasks.
If you are changing the structure and content of a static website, you should consider moving to a static site generator. Jekyll is the most popular. But I like Middleman. They give you all the power of an MVC framework or CMS, but instead of running on your server, they generate a static site ready to deploy to your server. You can use templates, they have an "asset pipeline" for your JS and CSS, etc. They are also great for repurposing content - it is easy, for example, to generate separate sites for desktop and mobile, or for web and app (e.g. Cordova). An SSG would be a great way to produce 'branded' sites as well. (e.g. same/similar site for different customers, but with different look and feel and some variations.)
