Lets say, I want an affiliate plugin that I bought for WP to work on Modx. What are the procedures to follow? Yes, you can assume that all the plugins I bought use php, javascript, and jquery.
You need to refactoring your plugin to modx snippets and chunks - http://www.cmslesstraveled.com/index/tutorials/refactoring-a-simple-php-application-for-modx.html