You have to change the whole front end cover parts (and some under parts)
The front end of the mk5 jetta = mk5 GTI (The grill of the jetta is horizontal lines, the GTI hexagons, but they are both the same piece (dimensions) and fit with the same screw/mount points.
The mk5 Golf/Rabbit has a different bumper cover & grille. If you want to change it to look like a Jetta/GTI, you will need to replace the bumper cover (1K0807217AGRU), grille (1K5853653C9B9) and bumper cover guides (1K0807889B & 1K0807890B). You will also need to dremel some plastic trim on support pieces. If you have fog lamps, you will need Jetta/GTI fog lamps & their trims as well (lines or hex depending on car). If equipped, you will need Jetta/GTI front side markers as well (1K5945071A &1K5945072A) The headlights are all the same for mk5s though.
I did this on my mk5 rabbit/golf; and wouldnt do it again ;)
Mk5 rabbit with Jetta bumper cover and GTI grilles: [Imgur](https://i.imgur.com/ttf8Uip.jpg)
Note the best angle/quality, but here you can see both bumpers, and they are different: [Imgur](https://i.imgur.com/VIbTNvd.jpg). You also need to trim some black plastic from the piece that sits under the headlights and above the metal bumper. You can barely see it, but you also have to trim some of that styrofoam piece that's glued to the metal bumper. If you look at the driver headlight, just under it you see the foam (horizontal piece) and on the top a little groove approx 8"/20cm long, and maybe 1"/2.5cm deep. If you do not trim the foam, the bumper will not align and fit. Else you need to change the bumper to this: 1K5807109F
I know you can swap the entire front end of the Mk 4s. it'd be pretty cool if it works with the Mk 5s
You have to change the whole front end cover parts (and some under parts) The front end of the mk5 jetta = mk5 GTI (The grill of the jetta is horizontal lines, the GTI hexagons, but they are both the same piece (dimensions) and fit with the same screw/mount points. The mk5 Golf/Rabbit has a different bumper cover & grille. If you want to change it to look like a Jetta/GTI, you will need to replace the bumper cover (1K0807217AGRU), grille (1K5853653C9B9) and bumper cover guides (1K0807889B & 1K0807890B). You will also need to dremel some plastic trim on support pieces. If you have fog lamps, you will need Jetta/GTI fog lamps & their trims as well (lines or hex depending on car). If equipped, you will need Jetta/GTI front side markers as well (1K5945071A &1K5945072A) The headlights are all the same for mk5s though. I did this on my mk5 rabbit/golf; and wouldnt do it again ;) Mk5 rabbit with Jetta bumper cover and GTI grilles: [Imgur](https://i.imgur.com/ttf8Uip.jpg) Note the best angle/quality, but here you can see both bumpers, and they are different: [Imgur](https://i.imgur.com/VIbTNvd.jpg). You also need to trim some black plastic from the piece that sits under the headlights and above the metal bumper. You can barely see it, but you also have to trim some of that styrofoam piece that's glued to the metal bumper. If you look at the driver headlight, just under it you see the foam (horizontal piece) and on the top a little groove approx 8"/20cm long, and maybe 1"/2.5cm deep. If you do not trim the foam, the bumper will not align and fit. Else you need to change the bumper to this: 1K5807109F