I am not sure exactly what you are trying to do here... the main text comparison methods available to you with calculation stages is InStr, with utility objects you have Regula Expressions available to you.
To compare character by character and then display the difference between two strings at a character level would require some kind of loop through the entire text comparing one character at a time.
It might be worth discussion this use case in more detail with your Blue Prism DEM.
