Going on a week.... )x<
The workaround is to manually add it to your Stat file, but the editor will not backread it and any time you edit the file via the editor your manual addition will be erased/overwritten.
That's because you're editing the .txt files. The editor generates .txt files from .stats files, which are just XML files, but otherwise does nothing with .txt files. You need to edit the .stats files directly, for this workaround to work correctly,
reload stats from the main menu/toolbar, and then make a temporary change to the tables you want to save so the Save button will activate. When you save from the editor, the editor will regenerate the .txt files. (Unfortunately, Save All does not regenerate the .txt files...)
The .stats files can be found in
Data\Editor\Mods\<your_mod>\Stats.
Related:
[Bug/Design] Editor does not refresh .stat files