This definitely cannot be done. When you run a Test Case
a new Test Run
is created and stored in the tfs database. The steps executed for this run and their result, comments, attachments e.t.c. are saved and cannot be edited.
From a test point of view, I think that even if you could do this, you shouldn't. Every test case should be as simple as possible so everyone can execute it. If you really need this, perhaps you should split the test case to two different tests, and the second one will have the first as prerequisite
.