If you owned a par-value MBS with a CPR of zero and rates declined, the decrease in YTM would be accompanied by an increase in prepayments (due to refinancing). The MBS with a zero CPR might then become an MBS with a 10 CPR. If so, what would happen to its price?

Alternatively, if you owned a par-value MBS with a CPR of 10 and rates increased, the higher YTM would be accompanied by a decrease in prepayments (no refinancing and less housing turnover). The MBS with a CPR of 10 might then become an MBS with a CPR of zero. If so, what would happen to its price?