We're using the scissors tool to open closed paths; this has been the most efficient way to change paths, in particular, ones with outlines like this half circle
We're not getting any error messages once scissors tool selects endpoints to delete that half of the circle
as you can see, by checking/unchecking Scaling Strokes and Effects we are constraining the stroke and effect when we scale the path. In this example, we have Blend on and by checking/unchecking, we are scaling the effect along with the path.
We have to make sure that scale corners is checked whenever we are scaling an object with live corners. i.e. the curved corner will not scale correctly unless this is checked.
To learn how to scale strokes& effects, read blog post:
File>Preferences> Selection&anchor display>"Hide Corner widget for angles greater than"
this hides the corner points for editing live corners in illustrator. this, however does not disable live corners when scaling object. to learn how how to scale curved corners in illustrator, read blog post: