Just curious -- Is Finn actually popular with any audiences? Aren't minor villains from the original trilogy more popular than Finn?
[Citation needed]
[Substantiation needed to show that marketing materials for films can be changed that quickly]
It's a poster. You take it to a printing press and ask for a few thousand new ones, it's NBD. If they didn't already have several alternate designs from before they selected this one, it's like an hour of mucking around in adobe CS to make Finn smaller and droids bigger, less if you have the original images on hand.