The 23-year-old will start at outside centre on Saturday when Ireland visit Murrayfield for the first of Scotland's two World Cup warm-up matches.
For Dewey it promises to be an interesting and educational afternoon.
His position might be considered the hardest to defend, and the challenge facing Dewey has not been made any easier by the fact he is set to go head-to-head with Brian O'Driscoll, arguably the best outside centre in world rugby at the moment, who will be playing his first game since aggravating a hamstring injury against Italy on March 17.
Dewey, who will move from troubled Edinburgh to Ulster next season, said: "It is a new thing for me but hopefully I can step up to the plate.
"We've been training really well and I'm looking forward to it.
"We've been doing quite a bit of work on defensive alignment, so now it is a case of putting that preparation into practice.
"I played outside centre against France at the end of the last Six Nations, and I felt quite happy with my defence that day, but obviously it is going to be a new challenge this weekend against Ireland.
"Frank has given me a few words of advice. He wants me to follow guys into the heavy traffic and look for offloads and things like that, so it's a case of trying to be more of a predator rather than playing my usual game of trying to bash through the opposition.
"It is really a case of trying to read the game a bit more and that will obviously help my all-round game in the future.
"I've been enjoying playing 12 but Frank wants to try me at 13 so we'll see how it goes.
"With a bit more practice I might learn to enjoy playing outside centre a bit more, and if I could play both then that would be ideal because you can't have too many strings to your bow - but I'm still eyeing up the 12 jersey."
At Tuesday's team announcement, Hadden spoke enthusiastically about Dewey's potential - but he also said that the centre needed to cut out some of the errors which he has been prone to in the past.
"He's said that a few times," Dewey admitted.
"It is a learning curve for me because I've not got too many professional games under my belt - but I've been given this chance, so it's a case of trying to minimise the errors, maybe hold onto the ball a bit more, and seeing how it goes."
Dewey will win his seventh cap on Saturday and said: "This is a great chance to get the team rolling into the World Cup.
"We had a couple of disappointing results in the Six Nations, and a win would really spur us on ahead of the World Cup."