I had to really think about this one. Usually if I hear someone say "Oh I'd love to trade places with so-and-so! Even for just one day" I can think of a bunch of reasons why I wouldn't want to be that person. Even for a day. But after a surprising amount of thought, this is who I came up with:
Betty White! I think she's awesome and I freaking love her. She's old so she can say whatever she wants - FUN. She's adorable and I'm sure people tell her that frequently - I could handle that for a day. And did I mention she's awesome? I mean, people started a facebook page just to get SNL to have her as a host. I'm sure that after a day of being Betty White I would have reasons that it's not fun to be her but right now, I can't come up with any.