What is the significance of this form of Sri Krishna at Udupi? Kindly cite authentic source.
In the Sri Krishna temple at Udupi, Sri Krishna is decorated (alankara) in different forms one among them is Durgaroopadhari Sri Krishna (which is asked in question). In this video, many forms are shown.
During navaratri (nine nights), Sri Krishna is decorated in feminine forms according to the days dedicated to goddess, like Durga, Lakshmi, Saraswati, Mohini etc.