No, I believe that either to keep your Y ticket or getting an L does nothing to your chance of getting op-up'd.

If I were you, I'd keep my Y and get a new roundtrip ticket. I don't know about HKG, but it's always been cheaper for me to get a roundtrip ticket from SUB than from YYZ (I usually travel on 826/7 and 780-1).

Why not get a J fare, I thought the OP said it was on promotion for $4500 roundtrip? (read it somewhere on FT just now)

CMIIW