The official terminology is called "downline".
Before the pandemic, cruise lines may allow you to do so. You need to make the downline request in advance (prior to departure) and complete some paperwork. Cruise lines may charge a fee (for example, Royal Caribbean / Celebrity Cruises was USD 65 per person).
After the pandemic, some cruise lines no longer approve downline, even if you are willing to pay for a fee.
Here is the reply from NCL previously:
Approval to embark or disembark mid-cruise may be allowed ONLY in cases of emergencies, for example:
1. Guests miss the ship and wished to embark in the next port of call.
2. Once onboard, a guest becomes ill or has a family emergency and needs to disembark the vessel.
No refunds or adjustments will be made for unused portions of a cruise. If any of our guests for any reason wish to not conclude their cruise, they may address this onboard.
With valid reason(s), you may embark or disembark at ports of call other than original ones. Please note that you MUST have valid travel document or Visa required for the country that you would like to embark/ disembark. Norwegian Cruise Line will not be responsible for any loss associated with itinerary change such as hotel, transportation or entertainment onshore which is not arranged by NCL directly.
And also be aware that even NCL approves it immediately on Day 1 of your cruise, there may be a chance that the ship cannot enter the port of Naples on Day 5 because of various unforseen situations (e.g. bad weather). If you have booked any hotels or air tickets from Naples, NCL will not be responsible for your loss.