…shouldn’t keep coming up in your script after pg 30. When you’re at sea in your second act, adding a new character or a storyline you haven’t set up feels like new energy, but it’s really an indication that you don’t know what to do with the story you already have.
By all means, if your story goes in a new direction that works, finish the draft and rewrite to replace how you started with what you uncovered.
New characters who aren’t set up at all feel very convenient. You can set up a latecoming new character easily, by defining the space they will fill as a need or an obstacle, or thematically. The Wizard of Oz uses both of those techniques.