On the other hand, I may be wrong.
And you are wrong:
First of all, Shorten files don't have built-in md5 hashes. (As a matter of fact, they nearly don't have
anything built-in. It's a really dodgy minimalistic format.)
SHN filesets are usually distributed with an external .md5 file containing hashes of every single file, the hash list in this md5 file is used to verify the set of shn files at hand.
Warlock is spot-on, the file format is not inherently taggable anyway, and affixing tags to the actual shn file would definitely not only screw up the md5 hash, but it would seriously throw off existing shn decoders and quite probably cause seektable support to break.
However, there is a way to circumvent those problems. A later version of the plugin will support SHN tagging by storing the tags in external .tag files (as apev2 tags for the tagging / developing nerds among you)
This will enable shn users to make use of what is considered the best tagging format available, while leaving the original shn files intact and making the tags very easily removable.
(only drawback is that you'll litter your harddisk with a bunch of sub-1kb files
)