It can be modified to carry an ICBM but that will almost certainly alter its acoustic signature. Besides it’s far slower than a nuclear-powered sub and just won’t have the endurance if it had to go at more than 10 knots underwater.
Since modification of a sub is not a matter of slapping on a “Sub Modification Kit” available at the hardware store any such on this sub would have been noticed by the Navy. Multi-month jobs on big ships does not go hidden.