The sedan fender vent grilles are indeed much more a pain in the a-s to remove than the coupe/cab's.
I do it pretty regularly and best method I've found so far (sedan & coupe) is get couple of cheap flimsy butter knifes. Good stout ones won't do, nor will the real push-sticks / pry bars made for body work type of things.... too thick.
First for safety sake line the fender edge around grille with masking tape, couple layers won't hurt. I always start at bottom towards door side and push knifes in maybe inch or so and gently push down on knife to pry up on grille as knife levers against fender edge. Don't just put knife in little bit or you'll just be prying on front half of the snapped together grille peices. You should start to see the little tabs that hold it in becoming visible and hopefully coming out tawrds you. And just keep working along edge same way towards front of car. If knife doesn't go in at all you're hitting one of the little tabs that holds it in, just move bit to either side. The holding tabs are small, maybe 1/4" max, there are prob. 10-12 or so around the grille total.
Once you get it out some it can help to use hands and pull up on it. Once bottom edge and at least a little of each vert. side is out the top should come out easy / drop down towards you.
Sometimes on those sedan ones when trying to take out the front half of the grille will want to spearate from the back - if it happens you'll know what I mean (it doesn't look like it is two pieces snapped together but it is) - it isn't a big deal b/c you can snap it all back together once all out, but getting that front half off won't really help getting the back half off..... it is the same deal whether front half is off or not.
I don't think there are lites on the sedan ones like coupe ones, with the light ones once you unplug it from grille you'd prob. want to be careful not to let wire fall down into fender unless you have a good flexible grabber tool.
As long as you put tape on fender you can't really mess it up that bad beyond maybe marring existing grilles, but if you're putting new ones in no big deal prob.
New ones should just snap right in. The coupe ones need to put front in first and then work back to snap in but I think on sedan ones doesn't really matter, prob. slip tabs along one long side in and then snap in.
And after all that those stupid grilles don't even do anything!! LOL Look cool I guess.
If you have trouble I have pictures of times of done it somewhere burried amongst million other pics, if you want see let me know I will find and post.
Now I will also tell you I have had numerous crumby Chinese knock-off ones people have given me to install that don't fit for sh-t.... not much you can do about that. It is an extremely tight and precise fit on the OEM ones.