I'd want to know more about the error before offering a definitive answer. If the math was incorrect because you decided one of the entries wasn't a valid component of the claim and you are now reducing the amount paid, I would tend to say it's too late and "final is final." If on the other hand you transposed entries on a ticket and it has less to do with the claim itself, I'd say yes. You'd really have to explain the change.
At the end of the day, if it's an honest mistake and meets the letter, spirit and intent of the Reg E claims process and your customer is fine with the change I would make it. If it is an "end around" to reduce the amount paid on a claim or indirectly have more time than was allotted to finalize a claim, I would not look favorably at a change.