PDOC to EBOK without converting?
I think most people are aware that some sideloaded mobi books show up under 'documents' instead of 'books' on the Kindle Fire. This problem is resolved by changing the PDOC tag to EBOK. The most common way suggested to do this is to change the mobi output settings in Calibre: you'll see the default is to tag [PDOC] which must be changed to [EBOK].
Here's my problem: it seems that the tag is part of the metadata. Even if it's something a bit more than that I can't believe it should require re-conversion if it's already in mobi format. Re-converting means substantial extra time used and the chance of changing the ebook's format for the worse.
So here's the question: Is there any way to change the PDOC tag to EBOK without re-converting?