Since most filters are a series of resonators of some kind or another, terminating them in a resistance other than the design resistance will probably change the filter characteristics. Consider a filter that effectively has an input that is a RLC circuit, where the R is the terminating impedance of the source. If you change R from, say, 300 ohms to 50 ohms, then the Q will be different. That will certainly change the skirts, and will also probably change the overall passband (since most filters are stacked up responses of multiple resonances).
