Just found this:
http://www.allbusiness.com/north-america/mexico/873392-1.html
"Senate Approves Legislation to Eleminate Dry Law on Election Day"
Wednesday, March 15 2006
"In a unanimous vote in late February, the Senate approved changes to the electoral code (Codigo Federal de Instituciones y Procedimientos Electorales, COFIPE), eliminating a federal prohibition on alcohol sales on the federal election day. The changes to the dry law, in effect for almost a century, will be applicable to the presidential and congressional elections on July 2, 2006.
Under the reform to article 239 of the COFIPE, restaurants and other establishments will no longer be subject to federal restrictions on the sale of alcoholic products on election day and the day prior to the election."
OK, this article refers to the 2006 Presidential and Congressional elections, but nothing about local elections, other than the very end, which is still not addressing Mayoral or other races: "The COFIPE reform retained a clause that allows state and local authorities to decide whether to keep the prohibition in place locally."
Haven't found anything recent on this subject yet, though I'm only searching in English.