In the circumstances you describe, I think I would have no hesitation in swapping the existing breaker with a suitable alternative. I would, however, carefully set out the engineering judgement that I employed to validate that all reasonable precautions were taken to ensure the equipment and connected circuits remained safe. 

There would be plenty who would swap it out without a second thought. If you are overthinking things, it was good to be reminded about this significant issue.

I think that the concern is entirely valid and agree with lyledunn.

You mention your employer, so as an employee (as opposed to contractor or subbie) you have nothing to worry about. I would interpret, "person" in the last full line of Note 2 to 536.4.203 to be the legal person rather than the flesh and blood individual, i.e. the company which employs you.

(Good title, BTW.)

I think that the concern is entirely valid and agree with lyledunn.

You mention your employer, so as an employee (as opposed to contractor or subbie) you have nothing to worry about. I would interpret, "person" in the last full line of Note 2 to 536.4.203 to be the legal person rather than the flesh and blood individual, i.e. the company which employs you.

(Good title, BTW.)

Thanks for your response Chris. If you had to reference this engineering judgement to a British Standard to back up the argument what particular items within 61439 should I be concerned with?

E95 said:

If you had to reference this engineering judgement to a British Standard to back up the argument what particular items within 61439 should I be concerned with?

I am no expert in this matter, but BS EN IEC 61439-1:2021 requires that the design be verified. There are 11 different items in Article 10.1, but they include temperature rise and short-circuit withstand strength.

As with BS 7671, there is a provision which makes anybody who modifies the original design assume the responsibility of the original manufacturer.

The short-circuit withstand strength might be tested (destructively) by the original manufacturer, but verification by reference to existing components is permitted.

Perhaps there is an analogy with car tyres. Quite obviously, they need to be the same size as the originals. Then they need a speed rating which is at least as high. However, they can be made by a different manufacturer.

I certainly do not think that a panel should be replaced in its entirety just because one component has failed. That would be wasteful, but it does need sound engineering judgement.