Okay, there are multiple ways one might approach relieving this particular feline of its fur suit. See
this thread for some scripts which can be used to alter the status of one or more contexts. I've just posted a variant which prompts for a context substring and cycles all of the matching contexts one step around the active / on hold / dropped state triangle. You could use it to quickly put all of the City A contexts on hold (or dropped, for even greater invisibility) and make the City B contexts active. I would go with the Errand : Costco : City A structure (and use it myself, though I don't have the multi-homed life problem).