to reverse the blend direction, you have the True/False toggles for each end.
You would either use _SplitEdge and _MergeEdge so the seam is close to the one of the spherical brep or alternatively untrim the patch first, change the seam point of the trim curve and re-trim. Below is one example using a patch surface similar like yours.
RH6_BlendSrf.gh (6.6 KB)
RH6_BlendSrf.3dm (123.5 KB)
I guess doing the seam alignment programmatically is more challenging 
c.