what happens if I change my ticket back to the original airport that I flew from?

Then it's not a transit and you stood illegal in China.

If the immigration catch you at the airport, you'll have a lot of problems.

When outbound immigration sees that you don't have an exit stamp next to your entry permit there will be significant problem for you. Even if you had good reason they won't believe you because of the well known fake ticket to Hong Kong game that people have played