I haven't been into the dome light on mine, but I did add flashing LED warning lights that are mounted on the sides of the plastic roof. On my 40 series, the access was by removing the roof rather than dropping the liner. (BTW, Kubota calls the dome light a "Room Light")
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You didn't mention the type of lights or where you plan to mount them. If you're adding something that presses into a cut hole in the ceiling you may be able to fish between the dome light and the desired location. There's a lot going on between the liner and roof, so you should probably remove the roof to look before cutting holes.
If they will be under the dash, you may be able to slip wires down one of the roof pillars.
The roof is lightweight but bulky to handle. I'd recommend a second person and two ladders.
Pretty sure the dome light is held by a couple screws that you'll see behind the plastic lens. Mine has three modes that are selected by sliding the lens - ON, OFF and AUTO (operated via door switches).
Sounds interesting - please keep us in the loop.