Editing WordPress is essential and cannot be avoided. One would need to edit WordPress files some time. Like when a WordPress user wants to change the theme of his blog he would need to edit WordPress files. More than anyone, more advanced users would perhaps even edit WordPress files to change themes than newbie users.
To all WordPress users doing or planning to edit their themes or any WordPress file, there is one thing they have to do first. They have to backup files first. Then WordPress users who are editing WordPress files outside the built-in editor should make their changes on the backup files.
On the other hand, those using the built-in editor still have to backup files. Editing should be done with care in order not to distort the code in the file. The Theme Editor makes editing WordPress easier. But as in using any built-in editor, the WordPress user should also first make sure that the file is “writable.” If the file is not writable, then one would have to set up appropriate file permissions to be able to make some changes. And if for any reason the site crashes, simply delete the edited files and use the backup files instead.
If there is no back-up, one would have to download WordPress, the theme and the other files that are needed. One would have to replace the corrupted files and start over. So it’s really a standard operating procedure to back up files first before making any changes. It does not matter whether one is editing WordPress offline or using the built-in editor, files should always be backed up.