Right click a folderClick the sharing tabClick Advanced sharingCheck Share this folder With the procedure above, (I have disabled simple sharing) the permission is set to "everyone can read" by default. I share folders often but I almost never use the default value. So, I want to change the default permission to something else that I often use, for example "A can read/write". Is that possible?

The default ntfs permission is set on the root of the drive and typically inheritied from every child folder underneath so defaults is possible for ntfs guess. For share permissions there is no way that I know of to set a share permission with defaults so every new share created will allow read/write.