you do not need to erase the string "Enter Code:". If your code is 1234 and your rule is looking for the entry: "Enter Code:1234" , then you do not need to erase the string. If you write your rule different than the one I made and your rule is looking for the entry "1234", then yes you would have to erase the string and replace with the code, but why do that.
Show your rule, if you wrote it like the way I showed there is no need to erase the string.
Another way to state it is that my disarm code is "1234", that is the number sequence that I and my wife need to remember to disarm with that tile. But the rule is not looking for me to enter "1234" in the tile's string,(in order to disarm the alarm), it is looking for me to enter "Enter Code:1234". I don't have to worry about remembering or entering the first part of the string "Enter Code:", since it is always displayed by the tile. I simply need to press the tile and add 1234 onto the end of the existing string so it reads: "Enter Code:1234", this is what the rule looks for and executes appropriately.