Good thread! I can really relate to this because of my recent personal experience.
Just in the final stages of hooking up a Jabsco compact head. However, what was originally intended as a simple head replacement morphed into replacing all of the hoses, plus a seacock. For good measure, the plastic elbows on top of the seacocks were all replaced with bronze ones; and a Y valve was added, to switch between overboard discharge and deck pump out.
The only things not replaced were the macerator pump (still works) and the holding tank. Getting access to the holding tank means removing the floor boards in the deep locker. To remove the floor boards, I would have to unbolt the macerator pump, which is directly above one side of the holding tank. However, it is directly under the fuel tank. Can you see where this is going?
Bottom line: if it ain't broke, I ain't going there.
Overall, this has been a great exercise. When we bought the boat, the PO couldn't tell me anything about the plumbing system. All he knew was that when he hit the toggle for the macerator pump, magic happened. Because I installed it, I now know how everything works, including how to lock out the macerator for trips stateside. I am definitely in my happy space.