If you want to use Or the comparison will get very long and annoying to maintain if the allowed parameter list increases. So I would use !Contains and list of allowed parameters (or associative array):
Names Default To Here(1);
myFunc = Function({myParameter},
	{default local},
	ok_parameters = {"Parameter1", "Parameter2"};
	If(!Contains(ok_parameters, myParameter),
		Return(Eval Insert("^myParameter^ not in list ^ok_parameters^"));
	,
		Return(Eval Insert("^myParameter^ in list ^ok_parameters^"));
	);
);
output = myFunc("Parameter1");
Show(output);
output = myFunc("notParameter1");
Show(output);
But you can use or/and also, below is one example (| means or):
Names Default To Here(1);
myFunc = Function({myParameter},
	{default local},
	If(!(myParameter == "Parameter1" | myParameter == "Parameter2"),
        return(Eval Insert("output some msg"));
	);
);
output = myFunc("Parameter1");
show(output);
output = myFunc ("notParameter1");
show(output);
					
				
			
			
				
	-Jarmo