Just to name a few stations that have maintained the same format or otherwise adjusted their format directions that have changed ownership over the course of time. Note: I don't have all the dates for each one. Rhythmics can be included as well.
KMEL San Francisco (1987-present) - Century (until 1992; owned this station from its AOR and top 40 days) > Evergreen (1992-97) > Chancellor (97-98) > AMFM (98-00) > CC (00-present)
KBLX San Francisco - Inner City (1979-2012) > Entercom (2012-present)
KMJQ Houston - Keymarket (till 1988) > Noble (1988-94) > CC (94-00) > Radio One (00-present)
WVEE Atlanta - Plough > Summit > Granum > Infinity/CBS Radio
WKYS DC - NBC > Albimar > Radio One
WHTA Atlanta - Radio One from its inception in 1995
KKDA Dallas - Service Broadcasting from its inception in 1976
KKBT Los Angeles - Evergreen (till 1997) > Chancellor (97-98) > AMFM (98-00) > Radio One (2000-08)
KPWR LA and WQHT NYC - both under Emmis from their inceptions in 1986
KMEL San Francisco (1987-present) - Century (until 1992; owned this station from its AOR and top 40 days) > Evergreen (1992-97) > Chancellor (97-98) > AMFM (98-00) > CC (00-present)
KBLX San Francisco - Inner City (1979-2012) > Entercom (2012-present)
KMJQ Houston - Keymarket (till 1988) > Noble (1988-94) > CC (94-00) > Radio One (00-present)
WVEE Atlanta - Plough > Summit > Granum > Infinity/CBS Radio
WKYS DC - NBC > Albimar > Radio One
WHTA Atlanta - Radio One from its inception in 1995
KKDA Dallas - Service Broadcasting from its inception in 1976
KKBT Los Angeles - Evergreen (till 1997) > Chancellor (97-98) > AMFM (98-00) > Radio One (2000-08)
KPWR LA and WQHT NYC - both under Emmis from their inceptions in 1986