How to modify write permission on current buffer in emacs?

After changing the file mode, and before doing any edit, run M-x revert-buffer to reload the file. If the file is now writable, the buffer will no longer be read-only.

Alternatively, type C-x C-q (read-only-mode). This makes the buffer no longer read-only. You can edit and even save, but you'll get a confirmation prompt asking whether you want to overwrite the read-only file.

To change the read-only status of a buffer, use C-xC-q (toggle read-only-mode). To change file permissions, you can run dired on the file's directory (C-xd), search for the file by C-s and use M to change its mode.

If the workflow requires to change the file permission of the buffer repeatedly, then having a custom function would help like the following.

This works only on unix machines(executes system command "chmod"

(defun chmod-plus-w ()
  (interactive)
  (shell-command-to-string (concat "chmod +w " (buffer-file-name (current-buffer))))
  (revert-buffer))