I don't understand what the new grill has to do with the oil filter. The oil filter's underneath the very bottom of the radiator shroud, just behind the chrome corner pieces. If you'd like to change the oil and filter while you have the shroud off to replace the grill, that'd be easier to get to the filter. Otherwise, I don't think it'll make a difference.
I installed an Irate grill. Doing an oil change afterwards is identical to how it was before the install. I don't remove anything associated to the grill, to remove the oil filter. Unless I am missing something different that you may be asking.