Quick answerThe traditional GTA Online clothing BEFF method cannot normally be completed with only one session. It needs separate C1 and C2 states on the same account.
Why is one normal session not enough?
BEFF needs C1 to hold one clothing state while C2 creates another. Closing the only session and reopening it normally does not preserve two separate states in the way the traditional method requires.
Some current setups may provide access to a second session without the player personally owning two physical consoles. That does not turn BEFF into a one-session method. If you cannot access two sessions, use another outfit method instead.
You can still use the free clothing drawable lists to identify items and IDs.
Question
Yes, you can plan and save ordinary parts first, but the actual traditional C1 and C2 combination still requires the second session.
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