There are many cases where teachers want to create a new class, but do not want to manually input student information. Here is a shortcut to create a new class from a shared student roster.
Create a new class in your account.
Copy the students you want from the shared class.
As soon as you copy the class, an option to "select the class to copy the students to" will appear. Transfer the students into the new class.
The students you've selected will now appear in the newly created class.
If necessary, you can leave the original, shared class.