AFAIK the legal way to limit subsidized tickets is that the specific "membership" required to get the subsidized fare is available to all EU citizens - for example in Warsaw we can get lower fare based holographic stamp available from the city on the basis of paying taxes in the city - i.e. it doesn't matter what passport you hold, it matters that your tax residency is in Warsaw.

And healthcare operates by your local health system reimbursing the system in country you were visiting - you need to have European Health Insurance Card on you, from your healthcare provider, which helps route the payments appropriately.