Hi Sneezy,
I realize you're only asking a question as to whether eggs are allowed or not, but this opens a bigger topic as to what we can/cannot add to the program. Please don't feel I'm directing this reply solely at you. It's a great question that should be addressed and discussed by everyone.
One aspect of Medifast is that it is a VLCD. (very low calorie diet), and by cutting back on the amount of calories you have a day, you lose weight. This is ONLY 1 aspect of the program and there are several other factors that make it successful.
Medifast has been carefully designed by dieticians and nutritionist as a balanced, complete program. It's constructed of a precise ratio of good carbs - good proteins - and good fats. This ratio is very important and if we vary too much from the prescribed relationships of this ratio, we can throw the balance off and lose the benefits of the plan.
It can become a very slippery slope to start substituting other foods into the plan. In some cases it "may" be alright, in other cases your weight loss could come to a stand still. It's best to adhere as close as humanly possible to ensure that the program works for you. Sure, there's cases of people incorporating things into the plan. Later on as you reach your goal and enter into transition and maintenance, this is exactly what you will be doing, but my suggestion for people that are in the early stages of the program is to stick as close to the program as possible.
In the case of eggs, they are a protein and "should" be ok as part of the "lean" in the modified diet. Personally, if i was to be adding eggs, i would probably use it more as a spice and crumble 1/2 an egg into my salad, and cut my 4-5 oz of lean meat closer to the 4oz number to make up for the addition of the egg. Also keep in mind that eggs are very high in cholesterol and are NOT heart healthy. Take this into consideration, if you have high cholesterol or a history of heart disease. I am not a doctor or nutritionist so take this advice with a grain of salt.
My only recommendation is to follow the plan as designed. We know it works.
Keep shakin',
Unca