There is a window of opportunity to change your swims and that is between the time that the entries are posted to the website and the deadline for entries as requested by the host club. The deadline time and date is posted in the meet package (there is a link to the meet package on every Commitment Form).
If you are asking to change your swims after the deadline or after you see the heat sheets, you are too late and it’s not going to happen.
Keep in mind, that there usually is a very good reason why you are doing an event. If you kept doing the same events over and over again, swimming would become dull and you would not progress. Ask your coach.