If you were overweight and trying to lose the excess, then yes, eating all of the extra 800 calories you'd just exercised off would be a bit over-indulgent, as it would slow down your progress towards your weight-loss goal. But from what you've posted here and elsewhere, you're not trying to lose weight, are you?
If you're trying to maintain a healthy weight or gain a bit to get you up to one, I'd say try to eat all the calories you're supposed to. Not by doing a 10 mile run then trying to take in your normal meal plus the extra 800 calories in one go, but if you have a rough training plan for the week you could try to schedule in the extra calories the same way you plan ahead for a run. I think adjusting your weekly calorie intake to cover your mileage is a more sensible and steady way of eating than doing a huge run then stuffing yourself afterwards.
If you know you're going to do a 10 mile run on Wednesday evening, you could add 200 cals on Tuesday night, 200 cals with breakfast on Wednesday morning or as a mid-morning snack, 200 cals for refuelling immediately after the run then you'd just have to add another 200 cals on to your evening meal. That would be an easier way to take in the extra nutrition you need and would probably not feel as obviously greedy or indulgent. Though really those terms and feelings have no place in your training diet, as emotional attitudes to food intake are probably something you want to move away from. Just think of your body as an engine you're fuelling, and the food as petrol. If you drive your car an extra 100 miles you don't think of it as being greedy for burning more fuel and needing refilled, do you?
And if after a few weeks of eating to refuel, you find you are gaining weight, you can adjust your per mile calorie allowance down the way a bit until you find what works.