You could make it so you only get a flap the first time you write a letter for a given spot, so you could write and backspace for the flap but now you need two

You could make it so you only get a flap the first time you write a letter for a given spot, so you could write and backspace for the flap but now you need two letters for the next one since when you "refill" that spot it won't flap for successive entries.