Some political conservatives might not, but no political conservative would support changing it by decree of the federal government.
But the belief that state judiciaries and the US Supreme Court are way overstepping their bounds, forcing new definition down everyone's throat, seems to be more fervently held by social conservatives than political ones.
By the way, I support the Federal Marriage Amendment as a political solution that gets the federal government more into the marriage business, only because impeachment is deemed overly nuclear at the moment.
I suppose a political conservative might believe in the concept that marriage was never legally defined (only assumed) to be between a man and a woman. Since the definition of a word is changing, the political conservative seeks to keep government out of it either way.