The person at the EC presentation who asked that question about flying at reduced speed and power, was told by the EC representative that there is no need for it. The factor of safety while flying at MCP will still be much greater than the regulatory design requirements.
However I think he might still push for it in the company, similarly to whoever dictated that the S61N should still fly at 110 knots, long after the short-spar blades had all been withdrawn from service.
He'd probably decree that reduced speed should be adhered to until all gearboxes get the new shaft. It would be a pity to penalise the aircraft with such a belts, braces and nappy pins approach when belts and braces will be more than adequate.