With Wp Auto Affiliate Links you can automatically add affiliate links to your old content. It will save you hours of your time. What you have to do is to access the plugin management page add the keywords you want your link to appear and then add the url you want the visitors to be sent when they click on the link. Your content will not be modified in any way, the links are added when a page is viewed only, so your content will remain intact and if you deactivate the plugin then all the links will dissapear. You can edit and delete your added links, set the maximum times a keyword is replaced on any page and you can select posts that you want to be excluded from the replacement engine.