As drages said, modding GC spectres is one of the hardest things to mod (or rather most tedious, since the game has animations for every single combination of armour+weapon). AFAIK, people who mod weapons normally just edit the large picture as you did and then reuse animations from a different weapon.
In case you'd be interested, you could work even on this which could end up being included in the game itself (the community edition, to be specific). For example, each crash-landed UFO has only one image (see e.g. in assets/tiles/UFO/lightscout), but it would be a nice touch to have more images with variations in the damage. Another thing I've wanted to include but don't have the graphics skills for would be a separate image with ground damage (see e.g. the picture in https://en.wikipedia.org/wiki/Xenonauts).