Our new home is almost entirely lit by MR16 - GU5.3 LED downlights that are too harsh for my taste. Snap-on solutions for the fixture don't seem to exist so I researched the bulb route.
Basically, you can replace the bulbs and look for a flood rating in degrees. 100bulbs.com says this for MR16 bulbs (YMMV):
- Narrow Spot: less than 10 degree beam angle
- Spot: 15 degree beam angle
- Narrow Flood: 25 degree beam angle
- Flood: 36 degree beam angle
- Wide Flood: greater than 50 degree beam angle
Soraa makes a specialized bulb with a magnet and sell interchangable snap-on lenses that offer different types of diffusion, although they seem to only offer 2 sizes of bulb (including the MR16) and seem to be about 10x the cost per bulb ($25-26, plus $5-6 per diffuser) of ones with fixed / built-in flood ratings ($3 - $4).