After about a year of satisfied employment (good evaluations), my department informed me I would be filling the job duties of a vacant position, which are not at all typical job duties for my position, on top of my current job duties. When I asked how I would be able to get it all done, they (not being familiar w/the actual work) minimized the amount of time it would take to perform the additional duties, and no overtime by the way. I ended up working off the clock to meet deadlines. Even though the new job kept growing and the additional duties were difficult to keep up with, I learned a lot (with no proper training or resources I had to figure it out myself) and actually enjoyed the work and my accomplishments. Long story short they finally realized it was a full-time stand alone job. But rather than offer it to me (they knew it was what I wanted) they are now preparing to either hire a new person, or give it to a newly hired employee and hire a new person for their current position. Plus I get to train that person. Is there anything I can do?

Are you a union worker? If so, talk with your union representative. If not a union member, then there isn't much you can do. This happens quite often, especially during these last 4 years or so of unemployment and very fast rising prices. Unfortunately, it will be happening even more in the few years to come. Companies are really feeling stressed as far as money, and will do almost anything to keep from laying off workers. It's very unfair that you did all that, with no overtime pay, but you did the work, and I am sure they appreciated it!
The only thing you can do is either continue going along with what your company says to do, or look for another job... which might be hard to find nowadays. Good luck

You can talk to the manager, talk to the head of human resource.

You can be kicked for working off hours, companies don't care and the only person you hurt was yourself. If you had told them it took more hours, or showed them that deadlines did not get meet that way, things may have changed better for you.

But talk to them, and if not, this is often how things like this turn out