yes - you can- because catalyst makes no distinction between the physical port type - ( i dont care whether the interface is midi rs232 or whatever you want ) in any of the midi or serial input triggering-
So you can send the equivalent of a midi command- over rs232
either notes or midi show control-
to run a preset or a cue - over rs232-
you just set the input port in the midi triggering device to the rs232 port-
for the formats of midi or midi show control messages - you need to look at web docs-
any midi note can trigger a preset
in hexadecimal - base 16-
the numerical values for note on 1 are
0x90 0x01 0x80 ( i think ... )
decimal 144 , 1, 128