Replace a Single digit in a string

I am attempting to replace a single digit in string in studio 5000. I need to take the 23rd digit and change it from a 1 to a 5 while the rest of the information remains the same. Is it best to use an "Insert" Instruction here, or will that shift the rest of the original string over and just add my information rather than replace the original 23rd digit?

You can move a new value into MyString.Data[23]. If you expand the string in the Controller Tags (monitor window), you will see that a string is made up of a length and an array of SINT's for the characters.