The flour mixture might attract rodents, especially if it "cakes" up...that said, if it's not an issue it should be fine if the rest of the mixture isn't too high in fats that would become available once moist.

The carbs would feed fungi and the sugars would feed microorganisms.

Mix it in well to avoid caking and rodent attractiveness...apply appropriate or sparingly depending on the size of your pile, how "hot" it is, and how quickly it can "work on" the amendment.

Expired?

I just baked some pre-packaged cookie dough, ten years old, last week. It worked fine.
How old is it?

The "use by" and "sell by" dates found on food products are meant to help the retailer keep moving stock. They are not meant to tell you that food is no good after then.
If theat mix does not have weevil larva crawling around in it it can probably still be used, however, it can be composted just as any other food you could eat can be.

Here is a link that might be useful: Use by dates

I wouldn't put it where a dog might eat it. I seem to remember that dogs don't do chocolate?

Kimmsr:
Thank you for that link, I greatly appreciate it.