I had a SP mc and applied for the SP visa as part of a 3bm, the SP app did not even go through and got automatically rejected from the system as I had a similar product. so seems you should really downgrade rather than just switch from mc to visa.
No, that's exactly how it supposed to work, now you call with the reference # and say that you'd like to close the mc and open the visa, ime it was much easer then a standered recon for a declined card, as you weren't declined, only was rejected by the system because of already haveing a sp, so once you fix that problem (by haveing them close the visa), it should be pretty easy