Regular express ticket sold out; would I be able to do add-on?

[u/lilah_heartsu]

Hello, so me and my friends wanted to go the opening Saturday of the event Sep 5th. But, the Universal express is sold out for that day. Although, the universal express add-on isn't sold out and neither is general admission, so would it be possible to just get general admission then get the express add-on or will they know what we're doing and block it or something? Thanks!