Promotion: Job Duty Change

My question involves labor and employment law for the state of: Wisconsin

I have been working (as a remote employee) for my current company for over 10 years. I work for a division that is in another state, with the home office in yet another state. I have been told that they will be taking current job duties away from me (within the next month or so) and changing them to another job that I am not interested in (same dept - just a different position). Others in my dept will continue to do this job, although, eventually, the work may be moved to another off-shore division. They see this as a promotion, but I do not. (I have had lots of jobs in throughout my career and I love what I do now. I know what I like and what I don't like.) I talked to my supervisor about this and told him my feelings (not angrily, just matter of fact). I told him that I have to love what I do for a job if I am doing it 40+ hrs a week and the direction they have put me in is not what I am looking for. No raise is part of this, but I would rather love what I do than have more money in a job I don't like. My supervisor said he would talk to his boss about my feelings, but I have not heard anything back and I sense that there is no option for me to stay in my current position.

My expertise is in a very specific area, which is hampering my search for another job. I am thinking about resigning from my job so I can go to back to school to get more marketable skills.

Question: If I do resign, clients of my company may contact me directly to do consulting for them, doing the work I love to do (become an independent consultant). Can my company prevent me from doing this? I can't find any initial paperwork I would have signed when I started employment with them (might be packed away in some boxes). I assume there could be standard non-compete language in it. It's not like I am doing this job and it is available to me thru my employer. I'm am being told I can't do this particular job anymore.

Thank you.