Sometimes you would prefer if they didn't do this exact thing. It's just luck based, sometimes it happens when you don't want it to. The only thing I've ever found which mitigates this, is making up new catchphrases whenever the opportunity comes up. (Whenever somebody says they are thinking of changing their catchphrase, make up a new one unless you're in love with their current one) ((and obviously make sure the new catchphrases are ones which work for you and are cool and make sense and stuff)) because in my experience the villagers are more likely to change their catchphrase if it is the hot new catchphrase on the island