I made a selection of wedding photos three days ago, and the date of viewing is set at the end of August. Now I want to change the content of my choice, and do a check and change, can I?

Generally speaking, you can't. Now that the film has been selected, it has reached the process of intensive design. It is definitely not possible to propose any more changes, disrupt the workflow first, or the staff has already started intensive design. You can communicate with the shooting agency, see if a few minor changes can be specific or ask your shooting agency.