For what it is worth - in my Amtrak interactions I haven't noticed a larger percentage of authoritarians in that role than in other customer service situations. There are and will be people in situations where they see the most important part of their interaction as enforcing the rule than of specifically meeting customer needs. My approach when I encounter them is typically the same:

1. Figure out if this is a common issue or more an interpretation of a boundary condition.
- If it is a common condition - e.g. everyone is trying to bring on bicycles that don't fit
- it can be more difficult than if it is a one-off condition, e.g. this is a rare time they encounter a bicycle disassembling and the instinctive response is "no"

2. Recognize early when it becomes futile to challenge their authority to make a decision...
- If you turn a confrontation about handling a bicycle into one where you are challenging their authority to make and choose rules - you've lost. Folks get defensive and the situation doesn't improve
- Always remain polite, but insistent. At times use quiet cues of your insistence. For example, rather than getting a rejection and going away - I would still be there with my bike since I still have the issue.
- Be slightly clueless if it helps

3. Turn things into a problem solving exercise and enlist their help
- While you can't over-ride their authority - you can appeal to their sense of helping to solve a problem. For example, if not getting on board means you won't be able to get home, I would point that out and ask for advice on how to avoid being stranded. I might turn slightly clueless and have them help me figure things out, e.g. perhaps ask if this could be done on the next train or it not why not, etc.

I'm not sure I will be successful but I can illustrate the techniques in using an entirely different experience I had in trying to do something "against the rules" but still getting through. In this case, what I was trying to do is cross the border from Poland to Kaliningrad on my bicycle...

1. I came up to the Russian border station with my bike and the immediate response was "no you can't cross the border with your bike..."
2. I stayed polite but also a little clueless, "why?" and using less Russian than I otherwise knew...I also stayed right there rather than going away.
3. As that conversation seemed to be stuck, the guards summoned back to their superiors and someone drove up in a car to the gate station
4. The supervisor carefully explained in English that this crossing was for vehicles and no pedestrians (or bicycles) were allowed...
5. I asked why once more but then quickly pivoted into problem solving mode. I pointed out that I was trying to get to Kaliningrad and didn't know how I could do this if the border was closed.
6. They tried to be a little helpful and made some suggestions, e.g. I could cross via train or with a car...
7. I was a little more clueless and explained I wasn't sure how I would do this or for example where I would find a car to cross...
8. At this point the supervisor became even more helpful in problem solving mode...they essentially went to the next mini-van driver in line and told him he needed to take me across the border.
9. The driver grumbled but as we introduced each other and I explained my goals (cycling across Russia including via Novosibirsk, his home town) we were best of friends two kilometers later when he let me off past the border.
10. In none of this was I ever impolite, visibly angry or challenging their authority. I stayed calm, insistent and appealed as someone who had a problem and they could help.

Now those aren't exactly the same situation but if I encounter an Amtrak conductor or others with their rigid approach to rules and particularly interpretation of them - I'll try a similar approach. It may not work, but hopefully it doesn't make things worse.