I'm buying a train ticket on the long-distance Amtrak Empire Builder train that runs Chicago-Milwaukee-...-St. Paul-...

I'm traveling from Milwaukee to St. Paul. All the saver tickets are sold out. Value tickets are sold out for Milwaukee-St. Paul, but not for Chicago-St. Paul. This means it cheaper to buy a ticket from Chicago and just get on the train at it's second stop in Milwaukee.

I found this similar question [Can you get on an Amtrak train at a later station?](https://travel.stackexchange.com/questions/35960/can-you-get-on-an-amtrak-train-at-a-later-station/35979#35979), which notes I need to change my ticket after purchase. It doesn't address the possibility of a fare increase, is there a possibility that Amtrak would charge me extra and make me change my Chicago-Milwaukee-Minneapolis value ticket into a Milwaukee-St Paul flexible ticket?
['https://travel.stackexchange.com/questions/46810', 'https://travel.stackexchange.com', 'https://travel.stackexchange.com/users/20576/']
I asked a similar question to an Amtrak agent a few days ago. Here's what he told me:

Officially, your ticket gets treated as a "no-show" and is "subject to automatic cancellation" if you haven't boarded the train within two hours of the originally-scheduled departure time at your ticketed station.

He said that if you're traveling without checked baggage & printed your own ticket, it's "very unlikely" anyone would give you any problems as long as you were on board within that two hour window of time.

If the train is running late, or you have checked baggage, things get more complicated & uncertain. Apparently, staff have a tiny bit of discretion to relax an official policy, and almost unlimited discretion to rigidly ENFORCE an official policy. So, if your train is scheduled to depart from Chicago at noon, and Milwaukee at 1:45, but gets delayed and doesn't arrive in Milwaukee until 2:05, you COULD be denied boarding if someone wanted to be mean, but it's unlikely to happen unless you give them an excuse to SAY "no". If you're on board the train, have a valid ticket, and it's within 2 hours of the train's actual departure from Chicago, it's almost *inconceivable* that they'd make you get off the train at the next station & leave you stranded. But if you showed up at the station in Milwaukee 4 minutes before departure with checked baggage & needed to have them print your ticket, they COULD refuse, and management would back them up (possibly giving you a retroactive credit for future travel if you got lucky, but nevertheless leaving you in a world of hurt at that particular moment).

Another issue: if you DO need to check baggage, they probably WON'T tag it for the earlier station on the return trip. They won't do anything to prevent YOU from getting off the train before your official stop, but any checked baggage will probably be going to your official ticketed destination whether you like it or not. That's not to say you might not get lucky... but if they refused to pull your bags in Milwaukee, or refused to tag them at check-in FOR Milwaukee, they'd be entirely within their discretion, and you'd be out of luck.
Amtrak terms and conditions state that if you fail to board your train as booked your entire reservation is subject to cancellation 

It's one of the first things detailed on the conditions of carriage page here.

<http://www.amtrak.com/servlet/ContentServer?c=Page&pagename=am%2FLayout&cid=1241337896121> 

If discovered that you boarded at the wrong station the conductor at the very least might ask you to pay the difference in fare, and possibly be forced purchase a whole new ticket.

You ask about changing your ticket.

All saver fares are non refundable, so you can't change the booking, however if cancelled in advance they will issue you an e voucher for the value of the fare. Value fares also have conditions about cancellation and refunds

<http://www.amtrak.com/servlet/Satellite?SnippetName=IBLegacy&pagename=am/AM_Snippet_C/SnippetWrapper&ibsref=seeTCdetails> 

You would then need to purchace a whole new ticket, and if the saver or value fares have already sold out then you will be forced to buy a full fare ticket