Question about custom capabilities

Is it possible to start with only one thing that needs subscriber access on the site – and not use custom capabilities. And at a later date to add things and to assign that first thing as a custom capability and give that custom capability to current users?

In other words, where custom capabilities will be needed in the future but aren’t currently needed, can that whole thing not be dealt with at the start? Or would it need planning — custom capability need assigning — right from the start?