KPIX was never anything other than a CBS affiliate before the Westinghouse - CBS merger.Maybe. If I remember correctly, Westinghouse had a longstanding deal with NBC. All of its TV stations were NBC affiliates.
The only unstable major affiliation in the San Francisco market was NBC, and NBC did that to themselves with the KNTV purchase after getting into a "urination match" with the DeYoung family by trying to force a low-ball price to buy KRON.