Handling Modified Without Checkout Files
If you are going to modify or delete a file under Perforce version control, the read-only status of such file should be removed. WebStorm takes care of automatically making files writable. However, you can change read-only status manually, which may happen in a number of ways; for example:
With the Clear Read-Only Status option enabled, you make a file writable using file system.
When a read-only file is opened in the editor, you double-click lock icon in the status bar.
You remove read-only attribute externally, using file properties.