Interesting,  I suppose it's going to depend a lot on the work situation.  Small company is likely to be a lot more flexible, but some large company with an actual IT department might give you trouble depending on their software policy.   Would 43 vs 55 actually make much difference if say you had other skills they were interested in ?   Anti-discrimination laws are generally about something you can't change about yourself (race, age, disability) and not something like the degree of skill you have at a particular task.  I am not sure that you could even make a sufficiently strong argument with medical record of carpal tunnel syndrome.  CTS has many causes and so you would first have to prove it was caused by typing using Qwerty.  Second, just about every computer has Dvorak already and the employer could simply argue that there is no discrimination since any employee with CPI can use that instead of Qwerty there being no documented evidence that Colemak is any better or more comfortable of an optimization than Dvorak.  He can also argue based on normal expectation of standard business practice.  You want to get hired for job for which the ultimately determining factor is typing speed, well insisting on using Colemak for the test is probably not as good strategy as increasing your Qwerty speed and then after you get hired see how to adapt so you can work using Colemak.

I'd have thought that if you are having trouble getting past the bureaucracy to install Colemak, the best course of action is to have a friendly chat with Occupational Health. Any organisation large enough to care about locking your workstation down so you can't install Colemak is likely to have an Occupational Health department large enough to give some weight to your request if you can get them on your side. They also have a duty of care to help you prevent RSI, not just not discriminate against you if you've got it.