Aseprite is free. You just have to go to github and compile it yourself (this is legal and completely intended by the Aseprite devs).
Also I am pretty sure you can use/run scripts in Libresprite.. not sure about its API capabilities tho.
Hope this helps! Check out develop.games (from piratesoftware super cool guys tbh).. I don’t want to assume at all.. but well.. itch.io and pixel art leads me to think that maybe you could use something like the above listed site!
Good luck, Have fun :)