Auto change page title while bookmarking a page
That seems like a very fragile thing to do.  If it works at all, you would still only succeed on browsers where the keyboard shortcut is ControlD.  It probably won't work on a Mac or on a mobile device.  It will probably break if the user interface is in a non-English locale with different keyboard shortcuts.  It would also have no effect if the user initiates the bookmark creation using the menu rather than a keyboard shortcut.

You should probably step back and consider why such a hack is necessary in the first place.  Ideally, you should design the page titles such that they already make reasonable bookmark titles.