Is it possible to change the metadata of an item after it has already
been imported and built, without re-importing and re-building the
collection?

In particular I want to use greenstone to help organize documents whose
contents I have not yet fully classified. I want to import the document
into a "general category" in greenstone, then later, after having understood
the document and all of its implications, update its metadata and reclassify
it.

Indeed, in general, after months or years, I will certainly be changing
and updating metadata of my documents, as I realize their relevance in
new contexts. But years down the road, I do not anticipate having the
original source from which I imported the documents.

So, what's the best way to update metadata on already imported and built
items for which you no longer have the original source?

Thanks,
-Norman