Wolf: there are some issues in which there are different acceptable opinions and some in which there are not. I will not go through each example you cited and state which category it falls under, since: a) I am not familiar with each issue & b) they were just examples anyhow.
To take one example you cited that I am familiar with, the issue of a woman wearing stockings below her knee: the Mishna Berurah clearly states that one only has to cover her knees and not below her knees if it’s not the minhag hamakom where she lives.
As far as I know, there is NO opinion that a lady does not have to cover her hair AT ALL. There may be different opinions regarding HOW or HOW MUCH, but there is no opinion that she does not have to cover her hair AT ALL!
Someone who takes a lenient opinion is not an apikorus. Someone who denies a halacha is.
If you know of any source that contradicts what I wrote, I would be more than happy to hear it.