Would Apple (UK) change a part with another for you? I was just wondering if Apple would swap my Optical Drive on my MacBook Pro for an SSD, and how much it would cost, as I would rather they do it and I keep my warranty then doing it myself and losing my warranty. I have AppleCare if that makes a difference, and the laptop is also still in it's 1st year warranty.
I would be supplying the SSD and bracket and cable and anything else needed to fit the SSD into the MacBook Pro.
I'd be very surprised if they would - there's no standard Apple product to replace an optical drive with an SSD. 

You'd either need to do it yourself using any one of the third-party optical bay solutions (see this question) or have a third party hardware repair firm do it for you. In both cases, however, you'd be voiding your Apple warranty as the optical drive is not a user serviceable part.