A little late on this one, but it’s been on my backlog for quite a while and I think it’s worthy of “public service announcement” status. Last week, Valve published a new Steam Client feature that allows users to relocate specific games to other folders. Just right-click on any installed games, click “Properties”, click the “Local Files” tab, then click “Move Install Folder…”.
So yeah, if you want to switch games to and from an SSD, the Steam Client can do it for you. You could always do it by shutting down Steam Client, moving the folder between two folders that Steam tracks, and restarting the client. I have experienced some situations where the Steam Client then looks at the files, determines that they’re invalid, and redownloads them. While I that just happened to align with a new patch or something, it’s a moot point now that Steam Client just does it for you.
So yeah, if you didn’t already find out about this: enjoy.