i don't know about AA, but on NW and CO, when the boarding pass is scanned at the gate, the reader will make loud obnoxious noises and point out your selectee status. at that point, the discrepancy might be noticed, and something more annoying than a secondary screening could happen.

i've managed to stay *CLR* so far on AA (tho i have been randomly screened..) so i don't know if AA's do the same thing.. just remember that the computer knows, even if you manage to alter your boarding pass...

i recently had a CO gate agent ask me about my ticket, then let me go without a screening when i got SSSS'd due to a last minute rebooking. she completely missed the SSSS on the boarding pass, but called down the jetway for me to come back up when the computer pointed it out.