2006.10.20 16:25 "Re: [Tiff] Modify XMP", by Phil Harvey
The harsh truth is that a TIFF file can not be edited after it is written if you want to preserve all of the original information. This is a sad fact arising from inadequacies in the TIFF specification.
There are various reasons for this, and people have invented very ingenious ways to try to circumvent some of these problems, but the fact remains that you always run the risk of losing non-standard/ proprietary information when a TIFF is rewritten.
- Phil Harvey