Can a master's student change their mind and look for a different project? I am a fairly new Master's student (~3 months). A few weeks ago, my supervisor told me to work on project X. I reluctantly agreed to work on X because I was not able to come up with any alternatives, due to my lack of knowledge in the field. 

However, as I spend more time on project X, I'm more and more convinced it's a bad project for me:


I'm not interested in X
I don't think there is a good chance of getting published (my supervisor and the other students agree it's a stretch).
I think my supervisor is mostly asking me to work on it because he thinks project X could become a business opportunity. I'm not interested in business opportunities right now.


I have expressed a desire to work on a different project, but my supervisor hasn't been willing to help me come up with one. He is really focused on making X a reality. I've come up with broad topics that I could look into further, but my supervisor always answers that I need to focus on X or else I will never get anywhere.

TL;DR My supervisor asked me to work on project X, and I reluctantly agreed. A few weeks later, I'm realizing that it was a bad decision to agree to X. 

Is it acceptable for me to tell him that I want to drop project X, and start looking for a better project?
Of course you can tell him anything. However, from your description, be prepared for consequences. If he is really committed to this project it is just possible that your speaking out will destroy any future relationship with him. If it is possible to change advisors think about doing that if it starts to go bad. You can't just work without an advisor and you need a good relationship with whoever you have. 

On the other hand, assuming he has more perspective on these things than you do, it may just be that fighting through your reluctance is the right course for now. Three months isn't a terribly long time if the project is significant. However, I don't understand why he is committed if he also thinks it isn't a good candidate for publication. 

But if neither option is available to you, it seems like you are just stuck. It isn't a good place to be. And not having another project to substitute it is hard to find a way out. 

Switch advisors if necessary, or push through it. It might even be that some small success in the current project will let you change your opinion about it. 

If you anticipate switching advisors, talk to another professor first who is willing to take you on before you make a break with your current advisor. Don't leave yourself unsponsored.