Are you sure about that? I may be showing my ignorance, but I never knew this, however I do check the charge indicator regularly to make sure my halon system is fully charged, and I carry a portable on board as well.
I would not remove the extinguisher from the boat unless I was absolutely convinced it was necessary. If you do need an inspection, wouldn't the courtesy CGA exam's done right on your boat be satisfactory? I looked up USCG Regulations regarding fire extinguishers and especially under 26', I do not see anything about inspections every 6 months! Attached is the link. Does anyone else have better info on this?
http://www.uscgboating.org/safety/fedreqs/equ_fire.htm