The most reliable thing to do is to replace the disconnect switch with a higher rating. At 230 kV, there is a great danger that could result if the disconnect switch could fail when it is already in operation.
Please review properly if the offered revision or modification is very reliable.
Siemens has an excellent testing facility in Berlin that can simulate severe earthquake. We have visited their testing facility but they will only test the high voltage circuit breakers upon request by the equipment vendor since the equipment under test will no longer be used. Usually, the...