Tijuana doesn't split into Tijuana and Ensenada. The report in El Financiero cited by Steffen Thorsen says:
"Para tal efecto se incluyen a los municipios fronterizos ubicados en la franja norte del territorio comprendido entre la línea internacional y la paralela ubicada a una distancia de 20 kilómetros hacia el interior del país, incluyendo a la ciudad de Ensenada, Baja California."
"To this effect [harmonizing the Mexican DST schedule with the U.S.], border municipios located in the northern strip of territory between the international border and a parallel line 20 km. toward the country's interior are covered, including the city of Ensenada, Baja California."
So we have the above indicating that Ensenada is covered. We also have the item from the government Gazette (quoted in the proposed changes) which gives a list of covered cities; Ensenada is not on the list. The Gazette item is from 2009-12-10; there may have been changes since then. I'll hold off on Mexico modifications pending clarification. --ado