It's not a big deal, from a technical point of view. It's likely I know the author and can get the sources, and if not, it's still rather easy to get out the graphics (pre-transparency) and recreate the dat from the data seen in the game.
It's more complicated morally/legally. Legally, if the addon is not under a license that allows changes, I'm not allowed to do any changes - even changes which are required for it to work again. Morally, the community frowns on those who try to rip pak-files. I'm inclined to do it anyway, in the firm belief that contributers want their work to be usable, but that's thin ice.
Either way, just give me the addon and ideally where it's from, and I'll see what I can (and am willing to) do.