Option to update existing references instead of creating new ones

I notice that if I import a bibtex file twice, I end up with two copies of each citation. It would be nice if the citation keys where used as a sort of primary key so that re-importing a file would update existing entities with the same citation key, if they exist.

My use case is that my users often maintain their bibliographies as bibtex files, which are used in many ways besiide being imported into drupal. They will commonly add or edit citations and re-import the file.