This is really straying from the topic of this thread. So if you have more questions, I suggest starting a new thread. But to answer your question, you just have to make sure that ComponentSystemGroup's base implementation of SortSystemUpdateList() is not called on your custom group. Then the systems update in the order you add them (it's just your standard C# List). Easiest way to do that is to override your custom group's SortSystemUpdateList() method.