Usually I'm relaxed in the morning, then go to work, enter a state of flow / complete focus, then at the end of the day I'm anxious (this becomes worse when I enter the supermarket for my evening groceries, even as I continue to think about work) and my breath is messed up (short, shallow breathing).
How would your method help here? For me it seems there is a contradiction, or not? Could you explain?
With that said, the CBT advice would be to recognize that thinking about your work in the evenings is causing you anxiety, so to stop getting anxiety you should refocus on the task at hand (shopping for groceries) and stop thinking about work. It's OK to let your mind wander while you shop for groceries, but CBT is about catching yourself when your mind drifts back to a topic which causes you anxiety (your work), and then using the task at hand (shopping for groceries) as a tool to basically distract yourself.
How you can make thinking about work cause you less stress is a different question. My personal advice is to try exercising after work, you'll feel very relaxed after. But if you're finding you're still stressed after work, my suggestion would be to seriously considering stopping your thoughts about work after hours (again, by catching that you're thinking about work and refocusing). Chronic stress kills.