Rental bike for holiday: wise to change handlebar style?
I'd recommend getting used to a new handlebar style (or frame geometry or any other change) slowly. On a multi-day trip problems tend to accumulate, so I would't recommend trying anything new. An additional problem with drop bars is that the brake and shift levers work differently and some people seem to have problems getting used to them.

You could try to rent a bike with drop bars at home and see how it works out.

Edit: For the kind of trip you are planning, many cyclists prefer drop bars. I would recommend trying out them if possible.