How do I make meh manse default to Celest instead of the plex?

You don't. It's evil and it kills unsuspecting shoppers.

But to be serious, I think it's to do with ships and where they're docked.

You can only do it for aetherships, because they default to where they're docked.

Unless that's been changed?

Ahh, okays. Well I'm buyin an egg anyway, so it's all good.