I don't think it will increase in frequency. It is listed as a new route for the summer since it has only begun flying in October (winter season). So strictly speaking, Prestwick only has 1 NEW route as of today, to Rzeszow.
Ibiza, Palma, Riga and Wroclaw are the only four routes to get frequency increases. Seems to be a mistake on FR website since Riga and Wroclaw are listed as new routes at the bottom of the page but it does say further up two new routes (RZE, WMI) and frequency increases on four (IBZ, PMI, RIX, WRO).
Wizzair will probably continue to compete with Warsaw-Modlin flying twice a week. They have had Ryanair ceompetition through the winter and they have recently put summer 2013 flights (up to the end of October 2013) on sale.