Practically yes, "legally", code wise, maybe. It depends on how your local code is written. And then there are usually requirements as to the sizes of the smaller vents and HOW MANY are needed to replace the larger one. That also depends on the interpretation of the code, for example, if the code says the "sizes" have to add up to the size of the original, then that could mean two 2" pipes were sufficient to replace a 4" one, but if it says the "areas" have to be equal, then it takes four 2" pipes.
Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County