This is a new save editor for Pokemon RBY, loaning its design (and a lot of its internals) from PKHeX.
Open or drag/drop a Gen I save file or a .pk1 Pokemon file, edit, then export the sav/pk1.
Currently (as far as I know) only supports US save files, from game cartidges, emulators, or the 3DS VC re-releases. If someone can link me to documentation of the JP save offsets, I'd be happy to add support for JP games.
Using the original RBY-style sprites can be toggled from the options menu.
Source Code is available here: https://github.com/SciresM/Rhydon
And you can download it here: https://github.com/SciresM/Rhydon/releases
More images: