Ultimately, to answer your question, I believe yes, tulpamancy is the practice of convincing yourself you are not all of the thoughts in your own mind. The first thing you have to do is overcome your parrotnoia. After that, other skills in tulpamancy are a matter of making new habits, adjusting your beliefs, or a combination of both. Without overcoming that first step though, odds are good switching won't help ease your doubt and it might feed into it too. I personally didn't find switching to help with our doubts.
However, even when confronted with that, does Rosa want to be you? If she wants that, then you may be happier integrating or embracing being median. If she doesn't, then you will remain separated.
The paradox of tulpamancy is what you or your system wants tends to become what is real. If you want a tulpa and you work for one, you will get one. If you have a certain idea about how switching works, usually that is the outcome of your experience. While there are obvious limitations to this, in general believing something is a certain way leads to it being true. (edited)