My original idea was to start a second FB page under my real name, kill off the FB page that I used with my dead name and just invite over the friends and family that I wanted to keep having contact with after I transitioned. (I keep my settings very tight, and no uninvited people can see my page anyways).
I've changed my mind recently, though. I've been on FB for many years and I don't want all those old memories to be deleted. After all, the people that I come out to will certainly know my old persona. It's not like I just beamed down from Pluto and started life on Earth. Why should I hide my past to people that embrace the real me? So...the current plan is to whittle down my Friends list to those that accept me, change the name on the FB page, and carry on.
Twitter is another creature. I've had two Twitter feeds for some time as I've been out in parts of my life and not others. Very few of my friends and family are active on Twitter, so it won't be too difficult to shut down my dead name feed, and carry on with my real one. Only problem, I've been busy making sure that all the feeds that I want to follow are followed on my actual page, too. Lot's of work!