Find something better to worry about.
First of all it is very unlikely that someone is going to try and smear you by either publishing this paper or keeping it for a number of years and then publishing. I don't know why you are specifically worried about this, but it's hard to think of many situations where someone would have a significant motivation to do this.
Secondly, even if someone does try and do this, it's unlikely to work. Information simply sticks around longer than it used to at the times of Barack Obama's birth certificate and Ben Carson's joke exam. If it's possible to find your paper, it's probably going to be relatively easy to find the nature of the assignment, details of the course, the contact details of other people who remember the situation, etc.
Thirdly, disclaimers and so on just will not protect you against a certain type of attack. If someone is really holding up your paper in the future as an example of your true but secret beliefs, they will easily be able to claim that the disclaimer is fake, that it was not present in the original, that its presence was itself a deception, and so on. These claims might be laughable - but so was the original one. This won't stop some people from believing them.
You might be someone with a very active imagination, who spends their whole time reimagining how their current actions will look when they are a presidential candidate in the future. Maybe you are simply indulging in a form of role-playing where you cut down cherry trees with your little hatchet, and then refuse to lie about it, and so on. I suspect however, that you simply object to having to write a paper from an opposing point of view, so you have invented this supposed practical objection as a form of protest.
In either case your energy might be better spent trying to develop your compassion and emotional maturity.