It is far easier to get a blunt nosed syringe for $0.10 (not sharpened for medical use) and use it to quickly and cleanly refill cartridges with whatever ink you want.
For a video visualization of how this works, Brian Goulet (who runs a popular fountain pen YouTube channel) published a tutorial on cartridge cleaning and refills: https://youtu.be/QloRQWHe5Gk?t=301
