Recite is a command line tool to automatically replace the citation keys in your LaTeX document when you replace a bibliography file. Very useful when merging work from separate documents with overlapping bibliographies that, chances are, refer to the same papers with different keys.

pip install tex-recite

recite document.tex old.bib new.bib > document.tex

the \cite{} commands in document.tex will be edited to match the citation keys used in new.bib

1. What if paper titles aren't exactly the same in 2 bibliographies or authors' names are off by a diacritic? Recite uses approximate matching with unisim, so similarly titled references will be matched.
2. Can't it make mistakes then? Yes, yes it can. But you do read your documents before submitting them anywhere, don't you?