Is an hiv negative test at 8 weeks highly unlikely to change?

Yes: Yes, however, current recommendations are to check again at 3 months.

Probably not...: ...especially if you have had a negative antigen-antibody (AgAb, "combo", "4th generation") blood test. These tests are conclusive at 6 weeks and no further testing is needed. If you had an older test, especially a 2nd generation blood test or an oral fluids test, get tested once more 3 months after the exposure.