thanks for all the feedback. I took a peek inside the ceiling liner, and yep, they are through bolted to nuts/washers despite
being plugged in the handrail too. I think I'm going to lag the new ones down since they're Iroko which is a dense wood, bringing the lags up from the inside and sealed with 4200. The old rails are too thin and course from too too much power-washing(blasting?) so there's no rescue for them.
AS for the ceiling panel, mine are in good shape, and yep, that starboard one is just too long! I though I might replace them with a lighter sheet of poly, or a textured fibreglass panel. Any suggestions there?
UPDATE I thru-bolted the new IROKO handrails, and cut the starboard ceiling panel at the " galley-turn" then put in a teak batten to cover the seam. The batten is positioned where two of the original screws are positioned, at the angled turn-out where the panel widens and goes aft over the galley. The batten lines up with the forward face of the galley counter. Future replacement will be easier, being able to cut both port and starboard panels from a 4x8, and a 4x4 of whatever I choose to use.