differential between charter
boats and owner's versions is based not only upon the layout, but the perceived differences in use/condition and the equipment
inventory. Most owner's versions will have less hours on the diesels/saildrives, more care taken in the use of the vessel (like a privately owned used car versus an ex rental car) and more comprehensive equipment
for cruising including better ground tackle, larger house battery
panels/wind generators, electronics
radios, etc. etc. In the end result, I suspect that an ex-charter boat that is converted from a four cabin to a three cabin layout will never have the same value as a legitimate, non-chartered boat with a 3 cabin 'owner's' layout.
Can a four cabin boat be converted to a three cabin boat? Of course, but IMO those who advise leaving interior
bulkheads in place are absolutely correct.
My Solaris Sunstream 40 had a 3 cabin layout (layout 'C') from the factory, which replaced the starboard forward sleeping quarters with a bath tub, shower, vanity and storage area. While there was a different molding for the shower sole and bath tub, all interior
bulkheads remained the same. Obviously similar modifications could be made to most boats, but care must also be taken before removing molded interior liners for the berths, etc. which are also often structural. This is probably why the molded liner for the berth in the 4 cabin version of the Sunstream 40 was replaced with a molded bath tub and tub surround to the same height in the three cabin version.