To add a plugin for only one NRO website, you need to do the following steps:
1) Have access to that nro sites controlling repository (For example, for GP Netherlands: https://github.com/greenpeace/planet4-netherlands )
2) On the develop branch, on the file composer-local.json , in the “require” block, add a line that will reference your plugin from packagist (for own developed plugins) or wpackagist (for 3rd party wordpress plugins).
4) For own developed plugins, please note that the version can be one of the following:
dev-before the branch name. So, if your branch name is my-nice-feature, in composer you have to reference it as
dev-my-nice-feature. This is only possible on develop and release sites, not on production sites
This will trigger your dev site to be rebuild including the new plugin.