Can I cook a slow cooker recipe on high instead of low, but for shorter time? This morning, I was supposed to prepare our chili recipe for tonight in the slow cooker, but I have forgotten.  Now it's too late to start the recipe as usual and cook it on low. 

However, it's not too late for my wife at home to prepare the ingredients and cook it on high for 4 hours instead. 

I know it won't taste exactly the same if we make it now and leave the slow cooker on high for 4 hours instead of on low for 8, but will it still be a safe, edible meal if we switch the cook time in this manner?  

Keep in mind, all the ingredients are either cooked or washed before being put into the pot, the only difference is the final cook time in the pot itself, and the temperature setting used on our slow cooker.
It will be safe and edible. It might not be quite as good.

Part of the appeal of slow cookers is just the convenience of leaving them unattended. The other appeal is low-slow cooking that blends flavors and melts connective tissue without burning anything.

Meat
Cooking things faster and hotter will not make the meat as tender as it would be- but it will still be cooked. If it is in small pieces the difference will not be as noticeable.
Obviously ground meat would be the same regardless of cooking time.

Beans (if you believe in beans in chili)
4 hours will be enough time to soften soaked beans. I'd say this is the biggest risk. Undercooked beans aren't fun to eat.
Soaked beans, canned beans, or no beans make this a non-issue.

Flavor melding
Chili benefits from time. Beans soak up flavors. Chili and onion balance out through the sauce.
I'll often make my chili a day in advance of serving it because it is so much better the next day. You're going to get less time so some of this will be lost.