Also,
There are methods which can be used which do NOT require a plugin. The same method works with html websites.
A simple php or html page which redirects the visitor containing the affiliate link. Like others have said, link to it using a no-follow and it is recommended to put the pages in their own folder and then restrict the robots to t hat folder with robots/txt.
If links need to be changed, there is only one place to change the link.
This results in a cleaner/leaner htaccess file, lower overhead since database calls are not needed to call the aff id, and MUCH FASTER visit redirects.
Rick
Universal4