I don't think that we should change the dictionary from upstream.
This is going to be a maintenance burden in the future when we want to upgrade to newer versions of the Open/LibreOffice dictionaries.

I would only be fine with it if we provide:
* a diff with the changes from the original upstream dictionary.
* a script that creates the dictionary from the original dictionary + the diff of local changes

Why not submit those changes upstream instead, so it would benefit not only to LanguageTool, but all other users of the Hunspell dictionary (Firefox, Open/LibreOffice, etc.)