No. Python Strings are immutable.
>>> s='355879ACB6'
>>> s[4:4] = '-'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment
It is, however, possible to create a new string that has the inserted character:
>>> s[:4] + '-' + s[4:]
'3558-79ACB6'
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