To be clear, in the scenario BCV23 outlined, the patron got ONE appetizer in place of their entree course (plus, perhaps, also had another appetizer, for their appetizer course). I doubt you'd be able to get TWO appetizers in place of the entree, plus your original entree.
Regardless, either way, such substitutions aren't guaranteed, and you may or may not be able to make such a substitution. Ask your server whether it is possible.