I guess maybe what you could do would be to make a blend factory, run .calculate on it, that should make a curve orientation list in input index 1, that then handles building the list and I think it will be possible for a script to modify an existing curve orientation list.

After the .calculate() or .update() that would go something like this:

// Grab the curve orientation list from input index 1.
var orientations = factory.getInput(1).getValue();

// This is an IMoiList which will contain 2 entries in it, each of which is a IMoICurveOrientation object.
// The IMoiCurveOrientation has 2 properties: .flipped and .seam - curve blendin will only look at the .flipped property so toggle that.

// Something like:

var orient = orientation.item(0);
orient.flipped = !orient.flipped;


Then recalculate or update again.

- Michael