I don't believe it's possible to completely prevent the user from doing this.
However, you could prevent the user from doing it inadvertently via the use of autocommands. Here's a rough proof of concept that ignores the new file name when the user attempts
autocmd BufWriteCmd * :w % | set nomodified
However, note that there are many ways that a user can save text to a file in Vim. e.g. If you also want to catch
:saveas, you're going to also need to look into the
BufFilePre/BufFilePost autocommands; if you want to prevent the user writing ranges of the file, you'll also need to set up something for
You might also want to start Vim with the
-Z argument. See
:help autocmd.txt for more details, in particular,
A sufficiently knowledgeable user could simply remove these autocommands, (and even if they couldn't, they could just copy the text to the clipboard!) so this will only be a speedbump for a someone determined to save the text elsewhere.