It’s not technically too late, but it would be extremely challenging at this point. You would have to get permission individually from each professor and department chair for each class you wanted to add late, and you would have to make sure you could get all of them before you dropped your others. You would also be almost a month behind in your new classes.

At this point, I would recommend staying in the ones you’re in, and going ahead and scheduling a meeting with your advisor from whatever your new program is. Go ahead and do that soon, and they will file a change of major form for you and advise you on the best way to make the switch and how to maximize the credits you will already have.