Frankly, we have done this many times. Both staying overnight in a port hotel when the ship is in port for extra days or leaving for a multi day tour on our own. We have done over the years a number of multi day side trips where we’d left the ship in one port and joined it days later in another. For example,, we left the ship in Dubai flew to Delhi, took a tour to Taj Mahal, went back to Delhi and then flew done to Mumbai to rejoin the ship. The trip with guides, flights and hotels cost us less than $1,000 each. We did the same thing on the same cruise in South Africa leaving the ship in one city, staying in a Safari park, and and then rejoining the ship in another nearby port. As Jan Cruz suggested above, we informed Oceania before the cruise and all as gone well every time we’ve done this. .