The OEM tune has headroom to handle more Mass Air Flow than the nominal maximum; it just increases fuel to match. A tune is only needed if you change something that alters the calibration of the MAF sensor (like a tubing diameter change) or that increases flow enough to push it out of range (like FI). While opening up the grill might provide cooler air to the intake, it won't change the actual pressure at the entrance to the inlet horn by much, so the airflow won't change by much either. In fact, there's a risk that opening it up will create turbulence in that zone, which could reduce airflow. Unlikely though.