I think it is necessary important that "Extension" be a separate renaming choice in the single-Rename dialog.

There are reasons for this in my experience:

1. having to drag scroll a long filename text just to get to the end of the name to edit the extension after it's dot

2. While drag-scrolling the name text, Android often would initiate an automatic Paste dialog which can be accidentally tappped

3. The system keyboard would try to auto-captialize a letter after detecting the dot which is normal behaviour but is unwanted when doing a Rename

4. By implementing this request, it would make visually seeing the file extension a lot clearer. Users can more safely rename a file without having to tough the extension in most user cases

Please Mr Glodowski understand this. Another user on Google+ has already raised this same issue.

Please see attached image or here: http://i.imgur.com/gYgcrUP.png