The responsability of circulating with a vehicle that abides by safety regulations is of the owners, not the makers.

You'll notice that even in the consumer auto segment (which, since run-of-the-mill consumers are not expected to be "experts", has lots of of ways to make sure that brand new cars are sold already pre-certified "road-worthy" because normal consumers don't have the know-how to make sure of it themselves), the actual car owners still have the responsability of having a periodic inspection done to the car and repair those things that stop it from being road-worthy and they cannot circulate with it in a public road if it's not compliant (at least that is the case in Europe).

Outside the consumer segment, I expect that the rules for trains are pretty similar to those for commercial aviation: the manufacturer has no responsability beyond a contractual one (i.e. the purchasing entity probably demands contractually that the vehicles they get comply with regulations, the parts they buy obbey certain specifications and maintenance done by a manufacturer-certified shop delivers a compliant vehicle) and all the regulatory responsability is in the hands of the owner (more specifically the "operator", as for example for leased planes the airline doesn't actually own them but they do operate them hence they're the ones with regulatory responsabilities).

The USA argument comes from the anti-circunvention legislation for software being part of the DMCA law, said legislation giving rights to the makers of the software to stop changes to it even in devices they do not own. Where such legislation does not apply there is no law forbidding somebody doing whatever changes they want to software as long as they own the device containing said software or have the authorization of the owner of the device whose software they are changing - the only applicable legislation here is Copyright and that only limits the distribution of the software, not the changing of it.

It's not at all unusual for Americans to argue that people can't legally circumvent software protections even in devices they own, because that is indeed the case in their country thanks to the DMCA, but expecting that to be the case in Poland doesn't make sense as the laws there are not at all the same as in the US.