With product changes the account history stays intact when either upgrading or downgrading. The only thing that really changes is the reward structure of the card itself with regards to earnings. This is assuming you meet the other criteria for the PC like minimum credit limits if its a Signature/Infinite product and so on.
It’s not just Wells Fargo. You really should contact Alliant to get an answer.
Key Bank for example is another one that “product changes” are not really product changes. They are new accounts. I have seen reports of this from other banks here as well.
Happy I started reading these forums! I just converted my Citi Premier with a $95 AF to Citi Double Cash card