One of the only things that has really bothered me about the bone-stock Grom has been those terrible squishy narrow footpegs that always feel like you're about to slip off. I had a pair of OEM titanium footpegs from a 2006 Yamaha YZ450f dirtbike laying around so I decided to see if I could make them fit.
First thing that had to be done was to shorten the shaft of the footpeg down to .895" or so (pic 1 is starting length, pic 2 is shortened)
Second was too remove some the factory Yamaha up-stop from the foot pegs to allow them to swing up and back in the factory Honda footpeg mounts (pic 3 shows the material removed).
Last step was shortening the OEM Honda footpeg spring by a coil to make it fit. The spring will not use the hole in the footpeg mount any more but will register against the wall instead and works great (pic 3 shows how much I took off).
Attached are a few pics that show the steps. You can probably do this with most dirtbike footpegs but the Yamaha ones are cool because they're cast titanium so they are light and a good width (and will make sweet sparks if you get them on the pavement!) plus they are very easy to find for cheap. They make a huge difference for me in control and would I would recommend the mod.