<t>Yes, you can still use a similar method even if T<t0.In this case, as you correctly pointed out, the strike P(r(T),T,t0) of the coupon bond put (payer swaption) is stochastic, because it depends on the short rate value r(T) at time T, but you can still find r* such that P(r*,T,t0) - P(r*,T,tn) - ...