The rules may have changed since, but in 2009 I simply presented my UK license in Vicente Lopez, paid a small fee for photos etc, took an eye and road sign test and the license turned up a week later, no other questions asked.
I did the same two years ago for renewal and added motorcycles, again with no questions asked, apart from them taking another photocopy of my UK paper long form DL.
For me anyway, it's been the least troublesome of all Argentine paper chases.