You need to evaluate the contents of the $atts array that is passed as a parameter to the callback function. I can't test this myself because I don't have anything setup on my dev server for front end editing, but I'd venture to guess that $atts contains the field ID that you can use as a trigger for and if statement. If field_id = 999, then do this, otherwise skip the code. Use the Kint debugger to test the $atts values.