If you only have AA Platinum status, you are not entitled to any AAdmirals Club within North America if you're only flying domestic unless you have an AAdmirals Club membership.
But as you are departing from Tom Bradley, it depends on whose lounge EI is using. If it's BA/QF or CX, I think you can get in. But if its a contracted lounge operated by another airline, then you may be refused unless you are holding a premium class ticket.
Once you hit Platinum, all existing reservations will be updated automatically with your new status.
[This message has been edited by Guy Betsy (edited 08-31-2002).]