No. As far as I'm aware, there exist no regulations regarding SETI interference (mainly because this is a private endeavour and regulations would need strong international political support).
As soon as Rosetta hits the surface, its main systems will be turned off, including the attitude and control systems, as well as the main transmitter, the latter in order to meet regulations aimed at avoiding interference on deep space network communications channels.
Sorry, I have no further info on what these regulations are.
From the FAQ (http://m.esa.int/Our_Activities/Space_Science/Rosetta/Rosett...):
As soon as Rosetta hits the surface, its main systems will be turned off, including the attitude and control systems, as well as the main transmitter, the latter in order to meet regulations aimed at avoiding interference on deep space network communications channels.
Sorry, I have no further info on what these regulations are.