Since Aseprite v1.2-beta10
you can add/remove extensions to/from Aseprite. Extensions are
distributed as .aseprite-extension (.zip) files and you can
manage them from Edit > Preferences > Extensions:
In Edit > Preferences > Extensions there is a "Add Extension"
button. You can use it to select a .aseprite-extension or .zip
file. After installing the extension it will be uncompressed in your
configuration directory inside the
extensions subfolder.
An extension/plugin is exactly the same as a .zip file but you can
rename the file extension to .aseprite-extension so the user can
double-click it in Windows Explorer or macOS Finder.
The content of the .zip file varies depending on the kind of
extension that you want to create, but at least they must contain one
file inside: the package.json file.
The structure of a .aseprite-extension file depends on the kind of extension: