The Australian skills expert takes over from Grand Slam-winning coach Mike Ruddock, whose resignation for "family reasons' stunned the sport.
Johnson is also hot favourite to become Ruddock's long-term successor, although family issues in Australia and the Wallabies' push for his services, working alongside new head coach John Connolly, are clouding the issue.
In the meantime though, Johnson intends to devote his energy towards a Lansdowne Road appointment with Ireland on Sunday February 26.
"At the end of the day, the person in charge has the final call,' he said.
"If I feel someone deserves a clip across the ear, for right or for wrong, it is my job to do it. It will be run in my way, and it will be run in a way that is fair.
"There won't be any excuses - we don't want excuses,' Johnson added.
"I think I work hard at the best of times, and pressure is only the pressure you put on yourself. I do my work the best I can, and if that is not good enough at the end of the day, there is no shame in that.
"I will just work exactly the same way. I will do it my own way - I won't change.
"It is not a job I coveted. It has landed on my lap for a three-game period, and I feel that it is appropriate for me to do it for that tenure and it is for others then to review it.
"If I didn't take the job in this period it would have been inappropriate for the team. It is the right thing right at the moment. I feel that right now, it is in the best interests of the team.'