Due to a change of plans its easier for me to get off at the stop before my ticketed destination. How will this affect my return trip?

As long as you're not checking baggage, it won't matter that you're getting off one stop earlier and it certainly won't affect your return reservation. Depending on what train you're riding, you may want to inform the crew of your desire to get off early. For example, if you're in a sleeper, the attendant may not open the door at that stop if he/she isn't aware that you wish to get off and assuming that no one else is scheduled on/off at that stop.

On the other hand if you're riding a corridor train where all doors open, then it doesn't matter and you don't need to inform the crew.

Amtrak doesn't keep track of when you get off (unless your final stop was after a connection, resulting in a ticket not getting pulled).

Either way, it will not affect your return trip.

It's OK to get off the train before your stop, but it's not okay to get off the train before it stops.

Amtrak really doesn't know or care. Only matters if it's a flag stop and you're the only pax (if you don't tell the conductor, s/he won't know) or a short platform and you're not in a car where the doors open (in which case you need to get to one that does).

Well.....sometimes they care....I remember traveling with mom and dad as a kid between STL and Independence MO just outside of KC back in the late 70's....we were going to see the grandparents, and just about Blue Springs MO, we stopped..and sat, and sat....apparently a freight train had derailed and it was going to be a while. We were only a few miles from the grandparents.....I remember after an hour or so, some guy got up and decided to entertain the train, by playing his bagpipes....after about 10 minutes of that, dad said "come on".....and drug us all to the vestibule, opened the door on the field side, and off we went.....the CO was a bit perturbed, and very vocal about it.....we took a cab from a gas station to the Independence station where we met Grandad, who had been waiting for quite a while! So, yeah they don't usually mind if to get off early, but they do prefer you do it at a station!

You can also pull the emergency brake and hop off if the tracks run close to your ultimate destination.

Unless your planned destination is the county jail, this probably won't work out in your favor.

The conductor complained when I made this request around 20 minutes ahead on the Starlight, even though he was riding in the crew dorm-sleeper I was traveling in. The train would stop at Richmond anyway, but I was asking that the sleeper door be opened. Aw, shucks....

He opened the door, but I'd suggest making the request an hour or more ahead if possible.

In the 70's before Amtrak stopped in ALY (Albany OR), I used to give two short pulls on the line running up to the hoghead just before approaching the ALY station.The train would come to a complete stop before resuming travel northbound, allowing me to hop off.
It sure beat having to make my way back from Salem.
I am sure these moves helped to put Albany as a station stop later on.
You're welcome