vim - save file with new filename: append to existing filename

Question

Is there a simple way to (in VIM) do save the currently open file with it's current name plus an appended phrase?

IE, from /home/affert/ type vim /data/folder/file1.txt

then save the file as /data/folder/file1.txt_BACKUP without needing to copy and paste the filename?

Context: I have a file that has full paths in it to other files in other folders. I use ctrl+W, ctrl+F to open the file in a new window. That's why I don't want to copy and paste. BTW, the folder and file names are a lot longer, so typing them myself is not a useful option.

Answer 1

:w %:p_BACKUP

For explanation see http://stackoverflow.com/questions/2233905/howto-get-full-path-of-current-file-in-vim.

Answer 2

Easy:

 :w %_BACKUP

If you need override:

 :w %_BACKUP!

The it gonna answer:

"filename_BACKUP!" [New] XL, XC written