So to correct just the tapered edge at the bottom of the car, without correcting the rocker, you're saying you'd have to drill in and pull it out with one of those slide hammers? Then bondo and paint to protect against corrosion?
Edit: as opposed to removing the interior panels and hitting it from the inside
i have never tried to get at the back of these rockers so i am not entirely certain if they can actually be pushed out from the inside. obviously that might be ideal, but at what cost? removing a seat, removing sill trim, removing carpet, pushing wiring to the side... lets hope you dont break any plastic tabs in the process. just to not really have enough force or probably leverage in the end to likely tap it out properly or evenly. you're still going to have to paint the face of it in the end.. it wouldn't be cost effective.
no one ever drills holes anymore. that is back yard.
if i were to fix this properly, i wouldn't touch the interior. i would remove the gti skirt add-on and clean that rocker guard off the bare metal, then feather my repair area out with a da. i could either tack weld a tab of sheet metal on to the rocker, or better yet, a couple. and then attach a slide hammer and start yanking it out from the outside. or i could also use a uni-spotter which is like a slide-hammer with a tip that spot-welds to the panel. don't forget that this metal is now stretched, and may need to also be spot shrunk afterwards. once straightened, clean residual weld off the panel and epoxy prime the bare metal. then fiberglass. then bodyfill and a two-part polyester glaze to prevent shrinking. can then apply a coat of primer and check your work. scuff it and re-apply factory looking heavy rock guard. re-prime and it is ready for paint.
it takes a skilled technician to create an invisible repair that should last longer than the rest of the rocker which, if my experience with rusty ass mk5s is accurate, should be not long at all! lol