No grill does not need to come off. There is a thread on here already on how to do this without grill removal.
if you plan to throw away the front emblems, pry off the red part of the letters with a little screw driver. You will break the little plastic mounting post for them.
Next you will see little slots of where the tabs that hold the silver part to the grill, stick a screw driver in there to release the tab.
to install - open hood and remove the wide plastic trim piece above the area of the radiator, one with vent slots. Push new emblem into place until it snaps. For areas you can not snap into place, I used the wooden end of a small hammer to provide pressure from the back side to help get them to click in.