First, is the map light required for night VFR under part 91? 91.205(b) and (c) list required VFR equipment for day and night operations, and a map light isn't on the list.
Second, is the aircraft airworthy for night VFR without it? That depends on what the POH says. I Googled a couple of 210 POHs and found wording like this:
The airplane is equipped for day VFR and may be equipped for night VFR
and/or IFR operations. FAR Part 91 establishes the minimum required instrumentation and equipment for these operations. The reference to types of flight operations on the operating limitations
placard reflects equipment installed at the time of Airworthiness
I believe that means the aircraft is airworthy for night VFR if it meets the part 91 equipment requirements, but it's also a reminder that you have to operate it in accordance with all placards (per 91.9). As far as I can see, the type certificate for the 210 doesn't include a placard requiring the map light to be operable. In fact, it doesn't seem to mention the map light at all. (Some more modern Cessnas have a detailed list of equipment required for airworthiness; see this question.)
So unless your POH says something different, it looks to me like you're good to go as long as you placard the light as inop first, or deactivate/remove it (and log that, if required). 91.213 talks about "inoperative instruments or equipment", which is a pretty broad description and it would be best to comply even if it's unlikely that anyone would notice or care if you didn't.
As for changing the light bulb, at least one POH I found includes instructions for the pilot on how to replace the map light bulb in flight. It seems unlikely that they put that in there only for pilots who routinely fly around with an A&P on board :-) Having said that, part 43 Appendix A only includes landing and position light bulbs in preventive maintenance, and AC 43-12A says that the list isn't open to interpretation:
Part 43, appendix A, paragraph (c) contains the Federal Aviation
Administration’s (FAA) list of tasks that meet the requirements of the
preventive maintenance definition. If a task or maintenance function
does not appear in the list, it is not preventive maintenance.
So far, it looks like you do need an A&P. But, there's a generic exception in the list of preventive maintenance tasks in Appendix A:
The inspection and maintenance tasks prescribed and specifically
identified as preventive maintenance in a primary category aircraft
type certificate or supplemental type certificate holder's approved
special inspection and preventive maintenance program
If there's a "special inspection and preventive maintenance program" (whatever that means exactly) for the 210 that includes the map light, then you would be allowed to change it without requiring an A&P.
In reality, I'd be willing to bet that 99% of pilots would just change the lightbulb themselves, whatever part 43 says. They could always point to the POH instructions as evidence that Cessna considers it to be preventive maintenance.