I came across this problem and solved it using Fen’s suggested method. When you get a struct from the array, its actually a copy. The array inside that struct is thus not the one stored in the outer array.
What you need to do is store the array that you retrieved in a temp array variable, add your new element to that, make a new struct copying all previous data plus the new array and replace your previous struct in the array. Does that sound like a lot of work? Sadly it is. 