Are there any modifications that need to be made to a jockey box, if pouring non-alcoholic drinks, like lemonade?

Yes, kegs are best pressurized with Nitrogen, rather than carbon dioxide, when pouring still drinks. Cold liquids can absorb CO2 easily when you are using a highly pressurized system, like a jockey or jumper box. So when pouring carbonated drinks, use CO2.

On the other hand, Nitrogen has a hard time being absorbed by cold liquids, so any still drinks should use an inert gas like Nitrogen.