I just converted 2 Preferred cards to Rewards+. On one of them I received a targeted offer to convert, the number didin't change, then I converted the second one. Number did change, but the points from the old card are still there, and they are not expiring. I wonder if I can get 2x 10% back on TYP redemption from 2 cards? If this is a case, I will convert my other 2 Preferred cards to Rewards+. I can still rollback my conversion until April 15th. I'm planning to book refundable hotel stay and see how many points I'm getting back, if any. Not sure if it applies to airline transfers as well, but the language only excludes "points sharing", and nothing else.
I'm pretty sure that conversion is not opening or closing an account, and will not reset 24 months clock. I was recently forcibly converted from Forward to Preferred and from Preferred Visa to MC, and none of the points expired, that means account was not closed.