Only the original Blue from American Express will preserve a Membership Rewards account balance. (The points will be converted to Membership Rewards Express, which cannot be transferred to any other program, but this process can later be reversed.)
ok but let's say the hypothetical customer has 3 amex cards that all retain MR (plat and PRG type) with one associated MR account, and only wants to convert one or two of the cards down at annual fee time ?