Most people who ask about command grabs in combos don't actually realize it's pointless. If you actually had known that, that makes your question even more confusing.
Now, being a competitive player myself, I don't know absolutely anything you can do with command grabs after your opponent misses a purple tech to begin with. It's not something I've ever worried about, because where I play people tech greens on reaction even in CS with the reduced window. Purples just don't hit unless they're counter, meaning out of combo to begin with.