That is no problem at all - all of my meal plans are super flexible, and also include vegetarian options.
If you have a food allergy, simple use the "food swaps" section of the Nutrition Quick Start Guide to interchange whichever food you are allergic to with something similar. Anything on that list of swaps is a great option!
If you don't like certain ingredients in a recipe, you may also use that food swaps section to use something you DO like.
As long as you're choosing foods and ingredients that are in their whole and unprocessed forms, you can't go wrong.