John makes a valid point that you can't turn an MSR into an MSR+ as they are completely separate animals, but within the MSR models, the serial numbers reached 4xx (from 1xx) and possibly 5xx. "blue" functions started to appear on the 2xx serial models, but changed slightly on the 3xx models. Even if Meridian supplied a new EPROM, you'd be missing the relevant legends on the face of the remote, so no advantage to be had. If you want a more up to date version, you'd be best to sell your early model and buy a newer model. They come up on eBay reasonably often.

Cheers

George