If I want to cash out my UR optimally and currently hold a CSP, can I PC to a CSR, cash out my UR at 2cpp using Points Boost, and then downgrade again soon after (say in a week or a month) to a CSP or a no-fee card or even close the card?

Would the CSR AF be pro-rated for however long I hold the CSR before downgrading again? Or do I have a 'free trial' period as this Reddit thread suggests?

(I tried to get a CSR but Chase denied me since they apparently restricted approvals earlier this month if you've ever received a CSP bonus before, even more than 48 months prior.)