When Boston Ballet hired Mikko Nissinen to turn the company around, no one quite knew how such a feat could be accomplished. The company had been in chaos for several seasons, and could not seem to shake its image as something of an also-ran in Boston’s estimable arts scene. So how is Nissinen doing, one year into his reign? “It’s clear that Nissinen’s push for change, however subtle, has had an impact. The company that performs next season will be vastly different from the one that opened last September. There will be fewer performances and a smaller administrative staff. More dramatically, four of nine principal dancers, or featured stars, will be gone.”