Technically, you should be calculating a new W&B and put it in the airplane's logbooks and operating manual. As a practical matter, few do that, when they yank the back seat of a 4 place, or pull or reinstall wheel pants, etc.
A quick story to illustrate: Just after I passed my first ATCO (135 charter) ride, for my first 135 assignment, I was asked to take a 182 to the A Bar A (that's A--A in brandspeak) ranch southeast of Saratoga, WY, to pick up the baggage of the heirs to one of the fashion designers (can't recall which--pretty unimportant to me!), while our chief pilot took the 310 there to pick up the people, and to fly to Denver so that they could catch their flight back to Paris or New York or wherever such "fine" people live. I arrived at the airport to find that the backseat and passenger seat had been removed, to provide room for all the anticipated baggage. The 206 was in the shop, so this was the substitute way to accommodate the need.
I asked about the new W&B and was told, "It's lighter." Oh. OK, but what about how to load it? "Use your best judgment." OK. With half tanks for the 250 mile round trip, the airplane was pretty light and sprightly going over the Snowies to the ranch. The pile of luggage was pretty daunting, though--amazing what one woman and a couple little kids "need" for a 2 week vacation at a fancy lodge. By the time I got it all in and tied down, the airplane was pretty packed--and a whole lot less sprightly climbing out of the airstrip.
At Denver, the Combs/Gates folks provided a van to haul the stuff to the gate, and the footman/butler/whoever for the family was there to greet me with several redcaps, to haul the luggage to their flight. Once the van was unloaded, he gave me a $20 tip! I guess that would be about $85 in today's money.
And that began about 10 years of part time SE 135 flying. Good fun, with lots of different experiences.
Cary