This seems interesting to me... the one question I have (that others here haven't asked, anyway), is whether 'permanent' means 'imutable', or if I can replace

This seems interesting to me... the one question I have (that others here haven't asked, anyway), is whether 'permanent' means 'imutable', or if I can replace files with newer versions? My use-case is a large shared ebook library where I sometimes replace files with improved conversions (updated cover art, smaller files, improved CSS or standards compliance, etc.).