Strings are immutable, meaning we can't change the values. Refer to the given example:

>>> welcome = 'Hello, John!'
>>> welcome[0] = 'Y'
TypeError: 'str' object does not support item assignment

As the strings are immutable; we cannot change an existing string. But we can create a new string that will be different from the original:

>>> str1 = 'Hello John'
>>> new_str = 'Welcome' + str1[5:]
>>> print(str1)
Hello John
>>> print(new_str)
Welcome John
>>>