Somatic Meditation Experience

I have a question about the episode How to Master your Nervous System for Productivity and Joy - Jonny Miller and the clip Embracing Positive Energy. In the practice described in episode 708, The Neuroscience Behind Breakups + Building Better Habits, and the clip Visualizing Success, if a person is instructed to try and feel positive emotions like joy, happiness, and excitement, is it fair to say that during the initial attempts to keep the body calm using breathwork when negative beliefs or thoughts arise, and while redirecting focus to the intention of becoming a famous singer, the person will probably only feel frustration and anxiety as the brain begins to adapt to this new belief and dissociate from the negative default thoughts? Moreover, only after consistent practice, when the brain has started to embrace the new thought—seeing the person as a famous singer—would they be able to feel those emotions of joy, happiness, and gratitude? Is it also possible to feel some of these positive emotions in the early stages while engaging in neuroplasticity, even amidst feelings of anxiety and frustration? Can one experience both positive and negative feelings simultaneously in the beginning?