After traveling with a tour group, can I come back without going with the tour group?

Of course you can

And you can ask the travel agency to book your own air ticket or train ticket to come back

The travel agency can also help you with the room you want to stay in during this period. You arrange it

When I go to Jiuzhaigou and Hong Kong, I will only go with a group

When I come back, I will come back after their group

They will provide air tickets

Book the room you want to stay in

The discount is the same as usual for group tours

Yes

But you have to agree with the travel agency in advance