Wing it. To wing it is to do something without preparing first.
Fly by the seat of your pants. The person decides as things happen, without a plan.
We’ll figure it out as we go. The start comes first, and the details come later.
Make it up as you go along. The plan is created while the work is done.
Course-correct. To course-correct is to change direction during a project, not after it.
Call an audible. To call an audible is to change the plan at the last moment. The phrase comes from football. There the quarterback changes the play at the line.
Throw it at the wall and see what sticks. The team tries many things and keeps what works.
Ship it. The work is released now, as it is.