You can use Cyberduck to edit Amazon S3 files locally and automatically upload them. This software can be installed on Windows or Mac and you can use your favourite editor.
If you need to edit files on linux, please visit this link.
Edit Amazon S3 files locally on your Windows or Mac using Cyberduck. Saving the local changes automatically uploads the file to Amazon S3. The screenshots below show how to setup, login, view and edit the files. Download and install Cyberduck (version 4.4.3 as of this writing). Download the S3 (HTTPS).cyberduckprofile.cyberduckprofile) file and open it. It should show you a window where you can enter your Amazon "Access Key ID". Once you do that, it will let you login with your Amazon "Secret Access Key".
Once you login, you should be able to view your files as shown below. Now you can edit your files in your favourite editor either by using the Windows shortcut Ctrl+K or right-click and select the program to edit the file. I made Notepad++ the default editor for my HTML files. Make changes as you normally would and save the files. The file changes are automatically updated on Amazon S3.