Normally a modify should be written like

modify($p) { setName("Mark") }

and in fact in drl if you try to use the name of the modifed variable also inside the modify block like in

modify($p) { $p.setName("Mark") }

it emits a compile time error. Conversely the executable model generator just ignores the modify statement and generates a model without it which is misleading. It has to also emit a compile time error.