Post development for nakamura wt 150

Hi,
I am currently developing a post for the above machine,but I have hit a problem, the machine is twin spindle , twin turret configuration.when I select a tool , say on the upper turret i want to output M code to select main or sub spindle..I have a spin_select token in the code generator this outputs M303 but I want M243 but I can't find where to alter this value as this function is not listed in the m codes in 'nc style g code and modality' section ?
does anyone know how to get round this issue?
Thanks,
Richard.