Alex Kidd is hard-coded to only unlock on or after Christmas Day. I'm no programmer but I imagine the data reads something like this.
if DATE is GREATER THAN OR EQUAL TO 25th December 2012 then Alex Kidd unlocked = TRUE if DATE is LESS THAN 25th December 2012 then Alex Kidd unlocked = FALSE
So soon as you connect to LIVE/SEN/NinNet then he locks right back up, but if someone's found a way to circumvent this I would love to see it. --- I'm the squash for your juice, I'm pure, I'm concentrate.