You have attributes or other fields required or available for selection on an event registration form. You want them to be required or available for the first registrant, but not required for all guests. For example, if your registrant chooses a quantity of 3, the fields will need to be selected 3 times. You want to know if it's possible for the fields to only be selected once instead of for all quantities.
The attributes or fields will have to be filled out for each registration that is selected. If 5 registration units are selected, then the attributes will need to be selected 5 times.
One alternative is two create multiple event registration units - 1 for the main registrant and 1 for the guests, which would allow you to make the attributes available on the main unit, but not on the guest unit. You would have to instruct users to select 1 for the main registrant, and then select the guest units separately.