The MNRR EMUs are not capable of operating on 25Hz catenary at any voltage. When that decision was made in a desperate move to stay with axle load limits (25Hz transformers are heavier by quite a bit becuase they need a larger core), many pointed out that this might prove to be a problem later. But since there was always the third rail option available it was not considered to be a major issue.
The only issue was the different kind of third rail, and that was addressed by designing a universal shoe that works on both over and under running third rail. They were tested and found to be satisfactory at least five years back now.