I did some very important research for you all. You're welcome.
Store in town here has imported some British Cadbury creme eggs. So I bought one. For science.
I can now officially report that they are still in that old metal wrapping (rather than the weird plastic shell we have now.) They're slightly bigger and taste slightly different.
Now I'm not sure most people would notice the taste difference but I do consider myself something of a connoisseur after all. I do miss the metal wrapping so that was nice to re-experience.
But yes, I have done the research and can let you know they're still yummy, even when flown (ridiculously) from the other side of the world. (And ever so slightly different)