With HeatlhFrame 2.0 and later, the method you described for dis-associating a test from its related Visit will work just fine - with only ONE exception. Not surprisingly - the example you provided is that one exception: vital signs.
We have corrected this bug for an upcoming bug-fix release. When that is available, you will be able to delete ANY links - period.
There is one more issue in your report that may be leading to confusion. Since you raised that issue explicitly in another thread, I'll answer the point there, and just refer you to my comments in:
http://community.recordsforliving.com/forums/thread/519.aspx Support Team.