✔ 最佳答案
I totally agree with Eric's feeling. Your schedule is too hurry... It can be worked, but you will be very tired at the end.
It's true that Hong Kong travel agency can only help you to reserve point to point reservation. If you need to change, they may not be able to help you. However, if your trip is broken into 2 single trip, they can do it.
First of all, you have to make sure if the train you plan to take is "complusory reserved". From Paris to Salerno Duomo Via Vernieri, you need to change in Milano, then again in Napoli. I believe the travel agency can help you make reservation from Paris to Napoli.
From Paris to Salerno Duomo Via Vernieri, you need to use "2 days" on the railpass. The train departed at 20:33 in Paris and arrive Napoli at 11:10 the next day. You can break it in 2 parts, from Paris to Milano and from Milano to Napoli. Then the agency may be able to help you. You don't need to reserve train from Napoli to Salerno Duomo Via Vernieri, since it's only a regional train.
Yes, you have to buy 1 day more for your pass if you want to reserve seat for the 1st journey... but it can also be treated as an insurance... same as your thinking, you will be standing in Paris if the train is completely full...