is it as simple as copying it into the plugin directory or do I need to register it first following the process outlined in the Wiki? If so, do I need to re-register it with each iteration during the development?

Not sure if you mean for the framework or for the authoring tool? But I can tell you that for the framework all you need to do is have a copy in the relevant subfolder of your src directory (src/components for what you're developing) and the $ grunt dev CLI task will automatically update the build with your changes as you make them.

This is why we strongly recommend doing any plugin development in the framework until you're as happy as you can be with how it's working - only then move onto trying it in the AT, as the process of updating a plugin for the AT is more involved.

It's not necessary to register your plugin during development - registration is about making it available to the CLI for commands like $ adapt install - and also to make it appear in the Adapt Plugin Browser - so it's really something you'd do right at the end.