Yea, it's kind of bad
As a general rule, what makes a wizard a powerful pattern is the way it simplifies the task for the user by breaking it down into identifiable recognizable steps, by appending an extra step the user might feel deceived or confused.
Given that not enough information about your context is provided, you want to probably do your best to maintain a clearly labeled static number of steps, any conditional content can be appended within the same step that enabled it.
You have no other option?
If you can't maintain a fixed number then you are dealing with a risk, typically when you create a new ui pattern, users try it, learn it, then they get used to it, however when you modify an existing one, you are contradicting the users expectations with something they are already used to.
So assuming you must follow this path, you can probably test it on your users then you will know the definite answer.
This is a great article that highlights how to implement the Wizard pattern effectively.