Do you have a copy of the AMX code that is loaded into the Axcent3 controller? If so the Axcent3 programming is similar to C++ and would require a string to be changed for the Video Command.
I would need to know the exact model number to give you the exact command, but it would look something like this;
SEND_STRING dvPROJECTOR_1, "$30,$30, $5F,$76,$31,$0D"
To switch command from Video 1 to 2 just change out the $31 to $32.