That's a 
For anyone else, this is the simple code I used:
using System;
public class NPCReplace {
  public static string NPCReplace(string InputData, char FromChar, char ToChar) {
    return InputData.Replace(FromChar,ToChar);
  }
}
Then I just use a Read File step before this, use {TASK(PrevTask,Output)} as InputData and define CharacterToReplace as \u0001 and ReplacementCharacter as a semicolon.
Note that this only works on single characters. If you want to replace more than one character you need to change the 'char' to 'string'