The Association of British Insurers only use a limited range of classifications for Eunos Roadster trim variations; you are not going to get one to quote you for a “RS-Limited”.
The ABI list the Eunos Roadster according to the following descriptors:
Mazda Eunos Cabriolet (1600, 1800, manual or automatic)
Mazda Eunos V-Limited Cabriolet (1800, manual or automatic)
Mazda Eunos V-SPEC Cabriolet (1600, manual or automatic)
If you think the car is worth more, in its present condition, than a normal 1800 Roadster, you could get the car on an agreed value classic policy (the car is old enough); generally, you need to get the car inspected by someone knowledgeable about that particular model, or cars in general. Some insurers will designate officials of an Owners Club, or Motor Engineers. I’d suggest to most of the latter, the car will be merely a modified Roadster, and for the former; well, you will probably need to join the MX-5 Owners Club, and contact their officials. Otherwise, in the event of a claim, you will be dependant on finding other examples of RS-Limiteds for sale, which have ranged from a cheap £1500 to a ludicrous £5k, and pleading your case, preferably with the car in your control (to avoid storage fees).
I had a 1993 M2-1002; there was no way the insurers could work out a UK value for it, though they put down on file that it was such as car. I would assume in the event of a claim, that would count for nothing. I certainly would not be expecting a £14k cheque as a compensation (the cost of buying one in Japan, and shipping it back). In reality, its UK value was not the same as a replacement value, since in the UK, I sold it for the equivalent of £2.5k
Insure it according to the way the insurers want it, enjoy the car, and avoid crashing it.
Paintcode should be on door shut sticker, engine bay VIN plate. M8 is obvious; its a green-blue colour. The door shut sticker will also indicate “RS” and the original Bilstein suspension package.
The door shut sticker will look like this:

The rest of the chassis code is merely indicative of the sequence of how the car came down the line, and contains no other information on the car. RoadsterRobbie is compiling a RS-Limited register, but I suspect the numbers will not be consecutive.