--- my_plugin.da.cpp ---

dsp_register_info my_plugin_A_info = 
{
   // variant A here
};

 dsp_code my_plugin_A_code = 
{
   // variant A here
};

dsp_register_info my_plugin_B_info = 
{
   // variant B here
};

 dsp_code my_plugin_B_code = 
{
   // variant B here
};


// etc., note you should define all of publish_microcode fileds for both A and B 
// (see fxlib.h for publish_microcode definition)

-------------------------

--- my_plugin.cpp ---

int iMyPlugin::request_microcode() 
{
	if (YOUR_CONDITION_HERE)
	{
		publish_microcode(my_plugin_A);
	}
	else
	{
		publish_microcode(my_plugin_B);
	}

	return 0;
}

// again stare at what publish_microcode does. In fact, you don't even really
// need publish_microcode, you may assign all nesessary variables directly.

-------------------------