Is there an easy way to do this?
For example (see attached image), if I have a house, and its forward direction is slanted as opposed to being aligned with its front face, can I select the front face and somehow set the normal of that to be the forward direction for the entire object?
I realize that I could always go into edit mode and rotate the object so that it faces the right way, but that’s not accurate enough.
Yes, go into edit mode and select the face whose normal direction you want to follow, now press Shift+S to position cursor at the selected face and Ctrl+Shift+Numpad7 or just Shift+Numpad7 to set view to selected and exit the edit mode. Now that you’re in object mode, Ctrl+A and create a Cube and choose Align to View in toolbar menu options. And from this point all you need to join the original object to cube with Ctrl+J in order to attain the cubes coordinates. You’ll have to be in local world space in order to move the object along it’s local axis.
I could make a video about this with a little bit extra information and a secondary way to to do this if you want. But tell me first, because I don’t want to waste my time on something that you’re not interested into.
Out of the box, Ognjen has the best solution I know of… Ctrl-J join it to a cube with the orientation you want. Then in edit mode delete the cube faces, and rename the object back to what you wanted. I’m sure there are more streamlined add-on solutions available. If anyone knows a good one links would be nice.
i think the best option for you is to alter the gismo. (the arrows you use to moves stuff)
if you do CTRL+ALT+SPACE. This will align the gismo with the normal of the selected faces.
@finalbarrage, that’s a great tip and a knowledge and grasp of how custom transform orientations work is critical for advanced modelling and might be just what this users situation needs. But, in the larger scheme, being able to realign the objects local transform to some other arbitrary orientation is also a good skill to have. 
