Coming back to answer my own question. I called Chase and the agent said that if I paid for taxes/fees with a CSP then the CSP travel benefits would apply even if I changed to a CSR before the travel dates. I'm not sure whether or not I believe that the agent knew what they were talking about. But I had DH call to pc his CSP to a CSR and they were able to confirm on the same phone call that the upgrade was complete and the CSR was showing on his account.
The rep may actually be right? This is a question that gets many answers but there are some DPs of getting the benefits at booking as long as the account is still open at the time of travel. I've seen it a couple times, just hard to search for... And after searching I cannot find the other comment that I remember that had more info.
If I can ever find it again I'll update. But it makes sense to me that what product terms you have at the time of purchase is what would apply at the time of claim, since that's when you entered into the agreement. What has always been a little vague for me is if you needed to have the same product at time of claim (or incident) as well or if just having the same account active is enough. According to that poster, just having the account is enough. If you read the benefits guides, they all mention the account as well. For example:
"You are eligible if Your name is embossed on
an eligible card issued in the United States, and You charge any portion
of Your Covered Trip to Your credit card Account and/or rewards
programs associated with Your Account. "
"Account – the Cardholder’s Credit Card Account issued by
JPMorgan Chase Bank, N.A. and/or its affiliates"
"Cardholder – an individual to whom a Credit Card Account has been
issued by JPMorgan Chase Bank, N.A. and/or its affiliates"
To be certain, better to have the same product on the same account at both points. But next best is making the purchase on the best product and keeping the same account open.