Hi Gra – firstly, welcome to the forum and your new way of life. Some people have commented that the calorie count on some of the recipes in the meal plan are not accurate, so I don’t know where that would leave you, re: mixing and matching, as I don’t know if the allowance for all breakfasts (or lunches, or dinners) are the same for each day. I’d suggest the best approach may be to workout the calories in the dishes you will be using and then you’ll have a picture of which meal options best fit together to achieve the 800cals per day.
Remember you don’t have to hit exactly 800 per day, as this is a marathon rather than a sprint, so there will be some days higher and some lower, but over the course of the 8 weeks it will balance out. I personally didn’t follow the meal plan at all, but created my own meals, but kept things simple, for instance – yogurt with berries and nuts/seeds for breakfast, salad and a protein source at lunch, protein source and veggies in the evening. However doing it this way, you have to calculate what your calories are yourself, but there are apps available – MyFitnessPal and FatSecrets for example – which will work all of that out for you, when you put in what you are eating.
Not sure if any of that answers your question or helps, but hopefully will give you something to work with. Remember to make good use of the forum too, as it’s a great resource for advice and support. We’ll be looking forward to reading about your progress, so best wishes for a good start on this way of eating.