I need to install an SEO plug-in first and foremost so that I can define unique <title> and <description> meta tags for each of my posts. I would be applying be applying the plug-in to an existing blog. In other words I already have posts and the posts are already linked with external sites.
Because my blog already exists, I am very reluctant to activate any plug-in of any kind unless I know what it will do to my existing posts. When I read the docs for all-in-one and platinum, it is not clear what they are doing automatically, and what not. I am afraid they will make changes to my urls, my permalink structure, etc.
Can someone who has done this already give me a heads-up/warning what the plug-ins do on activation?