Test Manager changing configuration back after completing a test case

I have a question in regards to test manager. I have set the configuration of the test cases from Windows 8, to four separate browsers, meaning in test it shows 4 test cases (1 for each browser). I want to change this though as it looks like overkill (and I am not really testing on all browsers per test case, just a few).

Is there a way to change the configuration back to just Windows 8 without the need of doing the tests again (as they have already passed)? It's like I need to select one to keep, change configuration but want that test case to remain in passed.