Is what you want.
From the docs:
set-visited-file-name is an interactive compiled Lisp function in `files.el'.
(set-visited-file-name filename &optional no-query along-with-file)
Change name of file visited in current buffer to filename.
This also renames the buffer to correspond to the new file.
The next time the buffer is saved it will go in the newly specified file.
filename nil or an empty string means mark buffer as not visiting any file.
Remember to delete the initial contents of the minibuffer
if you wish to pass an empty string as the argument.
The optional second argument no-query, if non-nil, inhibits asking for
confirmation in the case where another buffer is already visiting filename.
The optional third argument along-with-file, if non-nil, means that
the old visited file has been renamed to the new name filename.
This just saved me a few commands, hope you find it useful, fellow emacs-learners. Don't forget to follow the link to files.el and read the code for the function.