Threre are no rules on loadings, to my knowledge, just the mask requirement. It is up to the passengers to maintain the (1.5m) distance from each other. Deutsche Bahn long distance have even offered people who had train specific tickets the the possibility to use them anytime they like in the next few months.
As for the union element, I am bamboozled by the amount of minutiae that requires union approval in the railway industry, from the precise details of each roster, to the procedures for training staff on new equipement, to the methods of asssigning overtime. How do they even have the resources to check all this stuff?! Is there a full time 'shadow' union official for every manager that checks up on every decision they make?
In the 90s and 00s the railway, despite being an industry with a great deal of minute details that require to be managed to ensure it's successful operation, dispensed with a large amount of it's management experience following privatisation.
With management grades generally being in for little more pay than operational ones with much more mucking about there is little interest in progression in that direction from the shop floor.
Consequently there are a lot of railway managers out there who know nothing of operating a rail service. Not a single one of my current management team has ever done my job, and I'm not interested as someone who does a bit of overtime to afford a few luxuries in taking the paycut to have all the hassle including disciplinaries and on call.
An unintended consequence of all this is that much of your 'railway' expertise in terms of how things will work in practice with changes and new ideas, and particularly fairly technical things like diagrams, is actually gained when you run them by the unions for appraisal and it isn't at all unusual to have managers pop into the union reps or call them to ask 'what do you think about this?' regardless if they'd normally be consulted or not.
Just going by 'computer says yes' gets you things like a local service that is frequently curtailed or cancelled because the driver is scheduled a short cab environment break following working one of the worst performing long distance trains at the company.
The union can kick stuff like that back and say 'have you noticed this is a potential problem?'.
The same applies to building the rosters - the company comes up with the diagrams, they're run by local managers and the union reps to spot errors or make amendments with planning section having the final say and then the reps, who actually know how things go on the ground, build a roster to be approved by the managers.
Until you actually see it function it's hard to appreciate how and why it works and yes, there is occasionally some silliness over basic things, however for the most part it is beneficial for all parties.