You don't say how you made it into a custom command.  What you have would be appropriate to a menu item button in various places, but if you want to be able to type PLS at the Command: prompt, you need to define it using (defun ...), and within that, you can't use the macro-language form you posted.  It would need to be something like [I don't have the station-offset option, so you'll need to check the correctness of the option entry]: