вопрос про lein плагины уже похоже не актуален. Похоже проще всего плагин форкнуть, а дальше как в документации описано:
>During local development, having to re-run lein install in your plugin project and then switch to a test project can be very cumbersome. In order to avoid this annoyance, you can do the following:
>
>If you haven't done it yet, run lein install in the plugin's project directory.
>Just to make sure, run lein help <plugin-name> in your test project directory. A help message for your plugin should be displayed now. Or an exception originating in your plugin.
>Add the path to the src directory of your plugin to the file .lein-classpath in your test project directory. Probably you'll have to create that file.
>If your plugin depends on another library that you are also working on, then that needs to be added to .lein-classpath with the classpath separator, either : for unix, or ; for Windows. The same goes for your plugin's other direct dependencies. Run lein classpath in order to get an idea how the contents of .lein-classpath are supposed to look.
>Remove the entry for your plugin from the test project's project.clj. Otherwise it would override what you've added to .lein-classpath, because Leiningen loads those things before it loads plugins.