An informal amendment can be established by?
An informal amendment can be established by Congress via legislative actions and the President also has the power to amend through a clause in the Constitution.
An informal amendment is used when changes to an existing amendment need to be made if existing amendments need to be interpreted differently. Other examples include laws allowing gay marriage and laws that forbid whites to marry blacks. Each of these starts off as an informal amendment and, with time, are added as a formal amendment to the Constitution.