Sounds like a spell-check error to me. I think the remark is fatuous.
Boycotts are generally useless, but you can say "Merry Christmas" in reply to the "Happy Holidays" riff, much like your mother says "Yes ma'am?" when you forget and say "Yeah." Pretend like you thought they temporarily forgot the right answer. It will drive them crazy.
No it won't.
Greeters are not there to greet you. They're there to check bags, packages, coming into the store,
and to stop shoplifters from exiting though the entrance.
The greeter is merely a parrot repeating endlessly the phrase management directs.
It's rather hard to tell by looking which of the 100's of existing religions someone might or might not claim to be. They settled on a phrase which they believed to be non-offense to all but kookburgers.
They should have just used, "Welcome to Great Wal of China Mart"