YES. If your team that qualified for the SLC had fewer than the maximum number of team members allowed, you can add additional team members up to the maximum number of students allowed on the team.
Furthermore, if you need to change a team member, you may do that as well. The only contingency is that you cannot start with an entirely brand new team. At least one original team member must remain on the team.
Also see: Can I change team members from the group of team members that competed at the regional conference?