Hang / move large tv by myself? Is there a tool?

 Unfortunately, I occasionally find myself in a similar situation. If you do have the opportunity to get help, make dam sure they don't become a liability in the process! A lot of people have no idea how work together with another person and there is no time when an accident happens. Explain the maneuver Before it is being done.
 When there is no help and no other choice, I make sure that what ever plan I have is well thought out, often taking advantage of leverage, knowing that I can move an object in steps and not all at once. Making sure that the surface(s) used to help the TV down, are stable and dependable. It is not just the weight, but the awkwardness of the item in that the dimensions, lack of good handholds and balance of the weight of the item are taken into  consideration. Yup, get ahold of the heaviest end for best control.

Geek Squad is a pretty good choice, if you only have use them once. In this case it appears that the OP is going take time when the TV is down to do some rewiring and that sounds like it will be a couple of hours. More than likely, the Squad won't wait and would have to called in again for putting the TV back up.