Bread is basically just flour, water, and yeast, so it's pretty hard to make it inedible unless you burn it to a crisp in the oven.
The difference between all-purpose flour and bread flour is gluten strength; if you substitute all-purpose flour then your bread won't rise as high or be as strong; this is a desirable quality in, say, cake, but not bread.
However, AP flour isn't that far off from bread flour in terms of gluten; while cake flour may be as low as 6% and bread flour can be as high as 14%, AP flour tends to weigh in at around 10% or more, which is why it's called "all-purpose". As Michael says, yeast bread is actually not as sensitive to the exact quantities as (for example) most pastries, but it's still better to use a recipe that was actually built around AP flour instead of just trying to substitute it for bread flour.
If you are determined to make the substitution, then I would suggest you try to find some wheat gluten and add a small amount of that to the AP flour. Mathematically, if you assume that you're lacking some 3% protein, then you'd want to add about 1 tbsp of gluten for every 2 cups of flour. It's really not much, though, and if you don't have or can't find wheat gluten then your bread would probably survive anyway with AP flour, it just might be a little denser than you expect.
Butter flavored shortening and a touch of water (because butter has water in it too). The key thing here is that you have a have a solid fat because you're beating air bubbles into the butter during the creaming process. These bubbles are needed for the bread to properly rise during baking.
The browning process may be an issue though - shortening has no protein. You're after an umami flavor from the Malliard reaction ... it may be difficult to add that because of the lack of protein. A pinch of MSG maybe, for the umami?
Best Answer
Fat softens bread because it interferes with the gluten formation. It also gives the bread a richer flavor.
Many breads, including standard sandwich bread, include fat for these reasons. Butter has great flavor but any fat will do. You should soften any solid fats.
You can probably leave the fat out if there isn't much in the recipe. Expect the bread to be a little less flavorful and a little less soft.
If there is a lot of fat that is being left out you might have to increase the liquid to compensate for the dough being stiffer. At that point, unless you enjoy experimenting, I would just find a recipe that doesn't use fat.