my wife and I did something like this about a year ago.
I texted her from my work phone, so my name wouldn't come up on hers. I played it out like I was a secret admirer, chatting her up and eventually convincing her to meet me. Face to face, she told me that weekend she was going out with her girlfriend, and I told her I already told my buddy I would help him fix his truck.
When we met up, we did our best to act like two people meeting for the first time. we avoided talking about issues at home. Mainly focused on what we were looking for out of our "affair". During this date, I noticed my wife sat closer to me, and touched me a lot more than usual.
When the date was over I walked her to her car, as we had arrived separately. Before she got in her car, we shared a kiss that can only be described as electrifying, something we hadn't felt in a while.
Not long after she pulled away I got a text from my wife, "I need you to come home and make love to me!"
I would definitely say doing this put a nice spark back in our marriage.