Another great thing about digital, it's all in the the data. You're able to see instantly if people are engaging with your posts, or are taking the required action you need. It's not always about the target audience though, it can be your content strategy that needs to be changed. Unless your product or the market change significantly, I don't think there is ever a reason to  completely change your audience as that is often tied to the kind of product you are providing, most times you are looking at a more focused segment of the audience as oppose to a complete change - for example, I started off targeting black women for my makeup line, but now I have a new product that will make your eyes pop and look bigger, so whilst I am marketing generally to black women, I want to further target black women who have small eyes. Unless you reached the wrong target audience from the start, then you need a complete overhaul.