When I joined my current PhD program I talked to my advisor about wanting to work on a different research topic than the one I was to work on initially and he said yes. I made clear I wasn't interested in working on the initial topic long term.
A year has past and I talked to him about switching over to the topics I am interested in - he says "OK" but wants to continue funding from the initial project which is a large multi-university research project with frequent meetings. He wants me to continue to go to meetings associated with the first project and basically told me that we can jerry rig the funding into supporting what ever we want. This sounds good except the rest of the people on the initial project continue to think I am working on the initial topic full time and are expecting results. I'm not really sure how to handle this.
The outcomes I can see are.
The advisor starts complaining to me about not working on the "funded" research topic when the rest of the team starts complaining. If this is an issue, I will find a different advisor or exit with MS and enter into industry since I have no interest in working on the initial topic long term and I made that clear upon entering.
The rest of the team starts complaining to me about not making enough progress on the topic under the idea that I am working on it, when the reality is I have no intention to work on it and the advisor knows this.
Basically, I feel I am put into a difficult situation where my advisor wants to keep funding under the guise of working on this project while not working on it and I feel I will take the brunt of the inevitable blowup that will come eventually.
This wouldn't be a problem if the topic was broad in the funding documentation but the writing for my advisors role in the grant is very specific.